Who do you think it is?
If I had to pick one from the top of my head, it would be:
He's never really overwhelming in what he's supposed to do, and he has a high skill ceiling that rewards great players with fair treats.
Kitten of Evil64 votesI think 
is balanced, as far as midlane mages go. Immobile, squishy, entirely skillshot reliant, but a very strong passive and a ton of teamfight potential... and his mana costs aren't excessive.
ApexInTheCircle5 votes[{quoted}](name=Kitten of Evil,realm=NA,application-id=3ErqAdtq,discussion-id=2Yg2xKAf,comment-id=0004,timestamp=2015-03-10T00:50:24.527+0000)
I think
Put me on board for the Vel'koz vote. He is hands down one of the most balanced people in league.
BetaDude409 votesI had a game once where a Zed I was beating was trying to convince me that Vel was overpowered.
I'll just redirect him and any others here.
Protroid4 votesThe keep up on the Vel Koz train (The guy has been my main ever since I started watching my friends use him), the guy is one of a golden few that has not received a buff nor a nerf since his addition a little over a year ago.
But yeah, I completely agree. I've played a ton of games as Vel Koz and a ton of game against him. I just feel that something about using him just feels so right. The passive is strong but not easy to proc (unless you can land an E W combo, or the enemy laner stays in waaaaaaay longer than they should), his abilities, from Q to R are all varying levels of skillshot, and unlike many midlaners, he doesn't feel frustrating to play against.
Kitten of Evil7 votesHe's a last fading reminder of a golden age when champions weren't just fun to play but were also fun to play against
JC DarkOmen3 voteslast year? do you remember kass and leblanc last year, and pre-"nerf" lee, and pre-"nerf" zed (that AS nerf hit last patch hit him pretty hard, huh)?! this is ONE good champ in an era where everyone was freakin op as hell
Kitten of Evil4 votesOh I was more referring to new-release champions (after all, he was released in the same year as terrible-to-play-against 
)
SIayton2 votesI think Velkoz is a good example too. Incredibly damaging when you can land his skill shots but the opponent has full control to dodge them. He feels like what a powerful midlane mage should feel like. And if you're in your enemies head and know exactly where to put all your skills, well, you just get to melt them. I feel like if I'm better than my opponent play Velkoz, I can beat any champion. But I also feel like there's plenty of room to outplay me too.
Kitten of Evil3 votesYeah, there's something so satisfying about killing enemies with GEOMETRY! His Q and R are some of the most satisfying skills to land.
Martyrofsand43 votes
No champ in league has ever or will ever be as balanced as Orianna is. She should be the poster child for League as she is riots masterpiece when it comes to champion design.
TSM Dhinoo4 votesWTF Orianna isnt balanced. Look at the LCSbigplays last season
Acidic Puddle9 votesJust because she can make big plays does not make her unbalance. She takes a lot of skill to play
MakeHongKongFree29 votes
Do you know how hard it is to stay on top of that trident?
BetaDude404 votesI see what you did there
Kuroi869 votesI sea what you did there
Fixed that for ya.
IGotScuttleCrabs27 votes
Can be very versatile in builds. Full Tank, ap bruiser, full ap, 50/50 tank damage.
Can be played in most lanes
A skill shot that's very easy to dodge but has a high reward for landing
Strong burst and reasonable dps regardless of build
Has clear strengths (high cc and burst)
Has clear weaknesses (lacks mobility and hard to land Q)
DomainSpecific8 votesHonestly, as an occasional AP/Tanky AP Cho' Gath player, I would say he is not balanced. If you land Q, you will get a kill on any non-tank champion. If you miss it, you will get kited to death by any ranged champion while being unable to do anything. Having so much power locked into one skill is not healthy.
Zmuecat6 votesThat's balanced.
It's not reliable, but it's balanced.
76Summers14 votes
The Whamboozler8 votes^ This guy. Lux is almost always middle of the pack in terms of power. She can burst, but she's not really a hard nuking carry mage. She has utility but she's not a stunbot with nothing else. She has very defined strengths (Her range, her AoE Shield, her low Cooldown ult) and weaknesses (Immobile, squishy and 100% skillshots). She's got strong counter play to her, due to how heavily skillshot based she is. Playing her well takes skill. She's exactly who I think of when I think of a balanced champ.
terkmc13 votes
Clearly defined strength and weakness
Every single ability facilitate counterplay and descision from you and your opponent
Isn't opressive when ahead
Isn't useless when behind
Clear role and niche
Champion Skin1 votesIsn't oppressive when ahead Isn't useless when behind
Isn't that most tanks? As when they are ahead they usually aren't that bad as their damage scaling usually aren't that high And when tanks are behind they are of course still useful because... CC OP
terkmc6 votesHave you seen a Maokai thats 5/0 in lane? He will welcome your jgler and shove your top laner head up your jgler ass
MrPerson1012 votes
Oddly enough.
As far as AD assassins go, he doesn't have a safe playstyle like Zed does - has no real escapes outside of a short Dash, and takes a relatively large amount of skill to use well. Yasuos are a dime a dozen. A good Yasuo is one in a million.
Only Play Darius6 votesHe has two passives, both of which make him infuriating to lane against.
He is manaless, and has high-damage low-cooldown poke on his Q.
His ability to spam his dash makes him impossible to hit with skillshots.
He may have been nerfed to hell, but he is still infuriating to lane against as anyone who cannot match his mobility or poke.
MrPerson101 votesDisagree on the grounds that 
generally does great against him due to his high CD windwall, and isn't nearly as mobile, just has brutal combos.
Only Play Darius3 votesShe has mobility, poke, and is banned every single damn game so you can't use her to counter Yasuo.
DJ Di013 votes
As far as AD assassins go, he doesn't have a safe playstyle like Zed does - has no real escapes outside of a short Dash, and takes a relatively large amount of skill to use well. Yasuos are a dime a dozen. A good Yasuo is one in a million.
"I've been getting stomped in lane. But fear not! I bought Statik Shiv, so now I'll crit over half the time!"
Yeah; Yasuo's not OP by any means, but that kit is just awfully designed.
MrPerson102 votescrits also do 10% less damage, 25% less from his Q.
Really gonna complain about his crits over 
, the pentakill crit master himself?
DJ Di08 votescrits also do 10% less damage, 25% less from his Q.
Really gonna complain about his crits over
It's a /lot/ harder for Tryndamere to get his damage off than it is for Yasuo.
GigglingAngel7 votes[{quoted}](name=DJ Di0,realm=NA,application-id=3ErqAdtq,discussion-id=2Yg2xKAf,comment-id=0000000200000000,timestamp=2015-03-10T02:52:33.108+0000)
It's a /lot/ harder for Tryndamere to get his damage off than it is for Yasuo.
Luck 2 OP.
Plz nerf remove.
SmknWdl9 votesthe one that the balancing team hasn't touched
The Red Warden8 votes
has as many strengths as he has weaknesses.
Only cc is delayed but is powerful if triggered
Q has high burst but isn't instantaneous letting you get away from the auto
Laser is a slow skillshot but hits hard when it lands
Chaos storm has more counterplay than most ults.
He is also very immobile but that is made fair with his damage output. Once his gravity field has been used he is mostly defenseless.
SooFr0sty7 votes
is the only answer.
Hes getting his first set of buffs ever. :')
(I dont count his rework)
VardenSalad3 votesTrundle is balanced because he has so many unique interactions in his kit. I can't think of any other champ in the game who steals stats like Trundle does. Maybe Malphite with MS.
Look at these unique or very rare interactions:
Q steals AD
AoE ground-targeted skillshot that grants AS, increased healing(!), and increased MS only in its boundaries
E creates terrain
R steals Health, Armor, and MR both instantly and over time
These are crazy. Trundle probably has the most combined unique kit in League. The reason he's probably considered so balanced is both because he has so many levelers to tune (number-wise) if need be, but also because he's almost never been competitively popular, so he's never needed nerfed.
Awoof7 votesImagine, some (or many, not so good with timelines) patches ago, 
would have actually been a legitimate suggestion for this.
Time flies by...
Schteltzer2 voteshe still is
Stonington5 votesGalio because he has a 50.01% winrate.
femmé28 votes.01% op #nerf
Ancestor0073 votesUlt has now a .75 sec delay in which all enemies around you have 50% more ms so they can get out. Counterplay confirmed.
Kingsgrave5 votes
Anidan5 votesI like to think that 
is balanced right now. Not overbearing, I think. She's also not particularly weak. She has plenty of risk if she wants to go in, and when she goes in, then well, like Talon - she gets the kill or dies trying to leave in teamfights.
Failing her, then is pretty well-balanced. Seriously - even if I'm getting my face pounded in by him, I can't be mad. He's strong, but he can definitely be beat. I really cannot be mad at Vel'koz doing well.
SIayton3 votesJudging from this thread, it seems people find mages with skill shots balanced because there's tons of room for counterplay and avoidance, but also the champion is rewarded if they can land their skillshots correctly.
Long story short, skillshots seem fair. Point and click does not.
Champion Skin5 votesEhh... nobody seems to think Taric is broken though?
Toothierosprey32 votes
seems pretty balanced
Only Play Darius2 votesEver fought Rengar Top?
AbsoluteSadman8 votesAre we talking about 6 dorans blade rengar fuckyou top? Because that shit is not balanced.
Chaotic Reks1 votes
this motherfucker
by far one of the healthiest assassins in the game. he is gated by mana, has amazing (yet balanced) assassination ability (go in, take out the carry, get out). in the realm of assassins, he does his job very well, without being as overbearing as
Champion Skin4 votesThe problem with Talon is that... if he gets ahead... he can "assassinate" your entire team almost at least
GigglingAngel2 votes[{quoted}](name=NyX Reks,realm=NA,application-id=3ErqAdtq,discussion-id=2Yg2xKAf,comment-id=003a,timestamp=2015-03-10T14:16:13.007+0000)
by far one of the healthiest assassins in the game. he is gated by mana, has amazing (yet balanced) assassination ability (go in, take out the carry, get out). in the realm of assassins, he does his job very well, without being as overbearing as
Agreed. Sadly, because Zed exists, Talon is stuck in his shadow ... /pun