I can almost afford a 6.3k IP champion so now I'm deciding between 2 champions to buy- 
Vel'Koz and 
Rengar. So, I would like to hear the LoL community's thoughts about who I should buy. If you don't mind, please rate each champion like this in these categories (Out of 10):
Fun:
Difficulty:
Power:
Contribution to Team:
If you could, it would also help me if you add other stuff to rate these 2 champions on. Thanks in advance!
Hentai or Furry, decisions decisions. Jokes aside, I'd go for Vel'Koz. There's nothing more satisfying that watching the enemy team melt under your Ray. For Vel'Koz, I'd rate him; 8 7 9 7.5 respectively. As for Rengar; 6 5 9 6 respectively again.
Rengar Fun: 3 While picking someone and deleting them is incredibly satisfying and being stealthy is cool, he has a very linear playstyle with little room for fancy plays outside of bush hops.
Difficulty: 8 Learning how to properly manage your not-mana is the hardest aspect to learn for cat man specifically. Then comes the assassin playstyle which is pretty hard to execute. There's also the fact that he's so different from almost every other champion in the game.
Power: 9 A fed Rengar is almost impossible to stop if your team can back you up. Find the carry, blow them up. Rengar is an assassin which makes him a decent carry already and the fact that his ult becomes a delete button late game makes him one of the better ones.
Contribution: 2 Rengar is a much better champion when he takes every kill. He requires his team's backup but gives none himself. Assassins in general are very selfish and Rengar is no exception.
Risk: 6 While he is a very feast/famine champion, it's pretty easy to get ahead on Rengar. As long as you don't die to much early game and pick up a few kills you should be fine.
Vel'Koz Fun: 8 Maybe it's just me, but I think Vel has one of the most fun ults in the game. Laning can be hell against someone like Zed or Yasuo "shudders" but overall very fun. Also he's a floating tentacled eyeball so.
Difficulty: 6 His skillshots aren't that bad compared to someone like Orianna, but he has a lot more. (As in, all of his skills) where most Vels fall flat is the passive. You absolutely need to detonate it in lane or his damage will be very small. That can be hard to get used to.
Power: 7 Vel is pretty unique as far as mages go in the fact that he doesn't really need all that much gold to get going. A Liandry's will do quite a lot of damage as his passive does most of the work. He's also a great user of Frost Queen's Claim and has basically all the damage if you get a good e-w-r combo off in a teamfight.
Contribution: 7 Vel'Koz is very team oriented. He helps set up with his q and e and can follow up on his team very easily. As previously mentioned, he doesn't need too much gold to do damage, meaning that he can build support items without worrying about losing too much damage.
Risk: 5 There are a few champions that straight up hard counter you (Talon, Yasuo, Zed) that are fairly common right now, you should be able to do very well in lane against almost anyone. Even if you do get behind, sorcs and Liandry's should do quite a bit of damage with your passive so you can buy defensively if you get behind.
Tl;dr: I'd say Vel'Koz. He is one of my favorite champions and is a pretty safe pick. Rengar is a little boring for my taste but mapping your ultimate to the delete key is pretty cool.
KOZ baby... LAZR PPL 4 DAYZ!!!
rengo fun:2 difficulty:7 power:10 contribution:3 risk:6.5
kazzy fun:6 difficulty:7 power:6 contribution:3 risk:7
Fun:10 MY ABILITIES COVER THE SCREEN
Difficulty:5 The champs mechanics are easy to pick up, but learning when to fight and where is harder.
Power: 9 Your not a burst type, but you have range and ridiculous power at a spamable rate so GG.
Contribution to team: 9 High damage AoE ranged DPS
Fun:3 I either kill everyone so fast its not even a challenge or I can't even take out their adc..
Difficulty:0 Derp target squishy, use abilites, oh look im better than le blanc with my .3 second kill
Power: 10 Can assassinate tanks
Contribution: 8 Lots of damage, even the worst players are guaranteed to kill one person running deep into a 1v5 missing 3 bolas and targeting the wrong champ from ult.
Depends on what you prefer to play. One is specifically for lanes and one does best in the jungle.
Velkoz
I main velkoz and he is one of my favourite champions of all time. (Mastery 5)
Fun: 10 When a champion exists specifically to de-tilt you, you know its going to be good. At least for me, I play VK specifically when I'm angry and people need to be incinerated. 45% CDR velkoz is insane btw. There's not much that is more fun than channeling your inner Deathstar laser.
Difficulty: 6 He is all skill shots so if you suck at those you won't have a good time. I prefer to play skill shot champs above all others so this was a plus for me. Positioning is also key since you are a slow glass cannon damage dealer.
Power: 9 If I'm fed I carry the game. One ult can destroy a team and the lower the elo the more they clump up and allow you to kill them. A full EQW combo can destroy anyone. True damage is really good against all champions. DO NOT UNDERESTIMATE THE DAMAGE YOU CAN UNLEASH WITH A FULL EQWR COMBO
Contribution to Team: 10
Has CC, wave clear, and aoe full team damage, as well as poke.
Notes:
Very strong champion even if behind.
Works well with thunderlords burst.
Average build for me: 
He is easily counterable by 
. If you're planning to play him in ranked be sure to ban this little shit. Or else you will not have a good time. Its horrible.
OVERALL 10/10 Love this champ.
Rengar
I main assassins and mages so this is also a good choice for me although I don't main him.
Fun: 7 I really enjoy playing assassins so i like this champ. I've also been picking him up a lot lately when I am forced to jungle (mid main).
Difficulty: 8 Although he is an easy champion to understand, his kit is hard to master. Having enough stacks when attempting an assassination for improved net is essential for success, and managing that is a hard skill in itself. Not to mention that his early clears are not that great so you are reliant on ganks to snowball.
Power: 7 A fed rengar is scary. There's a reason why people get PTSD from seeing the (!) over their heads. He can assassinate a squishy carry no problem, but his ult is countered by pink wards easily if the enemy is good enough.
Contribution to Team: 5 Net has CC and can assassinate high priority targets. However, he is not worth much to the team if he gets behind. Snowballing is essential in most assassins.
Notes: His mana less abilities allow for long drawn out fights. Works well with thunderlords burst. Still learning to play him so cannot offer very much advice except for general advice on playing assassins.
OVERALL 7/10 Solid pick for jungle right now.
**TL;DR > but depends on the role you prefer to play. **
Good luck on the rift ^_^
Ask yourself
Lazors and Teamfight
or
Surprise buttsex and solo killing
i would go vel cuz...
fun 7/10
difficulty 6.5/10
power idk what u mean by this
contribution with team 10/10
and rengo is almost the same but does not have as much team play as an awsome vel would. vel just rapes in team fights.
get velkoz, rengar will probably get destroyed this patch as riot stated that they dont like the way he is right now (and hes OP)
I really don't feel like following guidelines, but based on my criteria on picking champions, I wouldn't buy Rengar given you don't know what he will end up being like after Riot gives him a gameplay overhaul or some major changes.
RR even admits how ridiculous it is that he still hasn't been changed in his current state.
Vel Koz is stated to get minor changes during the upcoming mage update, but they are minor.
I'd pick Vel.
rengod
fun: 8 (0 if he is on the enemy team and you just happen to be the adc)
difficulty: 6 (learning the one-shot combo takes a bit if practice, you have to cast all of your abilities mid jump)
power: 9 (as much is I love him, he gets fucked by 
)
contribution: 7 (you ult in, then it suddenly becomes a 4v5, unless they have the champions listed above)
risk: 5 (no comment)
