Viktor: Has the highest burst damage of the three, can land it pretty reliably. He's good throughout the game, but very squishy and immobile. His CC is delayed, and he has the shortest range. Epitome of a glass cannon mage.

Orianna: Strong laning phase, lowest damage output, pretty reliant on her ult to be relevant. She's the one whose most reliant on teammates as well. Orianna is pretty surviveable though, and a well placed ult wins games.

Azir: Best overall damage output, longest range, mobile, wall of doom. Has a very high skillcap and desperately wants allies who will play around him. Lack of burst effects. Prone to nerfs because he's overbearing in competitive play.

Balls? Beams? Birds?

Breh.

Raise your donger

Push the lane, zone off teams, punish missteps, and capture objectives.

That is the playstyle of the Dong.

# Be different

But since my post is completely useless, I'll maybe try to stay in the subject

Viktor is like, a burst champion with very low cooldowns, that's his strength. He's not as much a control mage as the others, more damage-oriented. Orianna is very obviously combo-oriented, she can single-handedly win a teamfight just with schockwave, but can zone out people with the ball. She does not slow that much, but she can be a mini-Lulu with her shield+ speed up, and can also slow (damn I feel I'm being too much captain obvious) Azir is the control mage by excellence. His ult is also excellent to peel for the backline. His dps is really strong too.

Orianna is your safest bet, she's been a strong pick every season, and her kit is so solid that she won't be hurt by a few numbers adjustments if Riot decides to nerf her, she'll always have good scaling because of her short CDs and great utility.

Azir is strong if you're good at him, but he's probably the most likely to get nerf hammered considering his patch history and his current state.

Viktor is boring AF in my experience. His entire kit is you mash a few buttons and people die. He's highly susceptible to being nerfed to trash tier through just a few minor number adjustments because the only thing he really has going for him is facemelting burst.

great waveclear, provides constant dps in fights with his soldiers, can destroy towers fast enough and make his own, Ult is great at making picks and changing the flow of a teamfight, one of the best lategame scaling mage, great zoning with his soldiers dps especially with nashors and rylais make his soldiers really annoying to deal with. Cons to him are very hard to play you need really good mechanics to be good at Azir, relies on soldiers for dps, not enough burst damage like a lot of other mages, has a history of getting nerfed tho while still being frequently used in competitive tho soloq is far different compared to competitive.

has good waveclear aswell, can shield herself and allies, her ultimate can practically win a teamfights if you land the ball in the right place especially if you land your ball on you main engager like say a malphite with a ori ball on him than he can just ult and ori right after,her passive is pretty nice for csing, great zoning with her ball. Cons would be her ball can sometimes be easy to predict where its going, need to keep track of your ball in fights since its your main tool of damage not much else I know about her since I don't play her but that's what ori has.

has great waveclear get your hexcore upgrade to your and just clear the wave, great burst damage. Good zoning with his laser, W , and his ultimate, seriously people underestimate his W a lot. Great lategame scaling mage that is still good at other parts of the game, flexible item path even tho has 2 spaces filled by his boots and his hexcore just give him a rabas and void staff and just fill in what you would like. Cons for Viktor would be he is gold reliant needs his hexcore to help him scale tho they are 1k gold but still, can only build really 4 items not counting boots and hexcore, no real mobility and his gravity field can be easy to maneuver around at times, E can be a pain in the ass at first aim to but with practice it gets easier, No real way of defending himself besides his W, only form of waveclear is his E so once its done that can be your moment to poke him down.

Orianna is the best mage if you can play her effectively.

my main mage is she brings plenty of CC to the fight and has decent damage plus wave clear and she has a passive that lets her cast a free spell and she has a better version of as her ult

Oriana is the best teamfighter, and can shield carries. Her ult is great for wombo combos. Her main weakness is all her moves are telegraphed. You can see her ball and avoid it. Her shockwave has a substantial casting animation that you can flash/ult/shadow out of. That said her e gives her a large shield, and some armor making her somewhat resistant to assination. Viktor does the most burst damage of the three. If farmed, he can instantly kill your adc with his combo (or you if he lands all his skillshots). He has great waveclear/pushing power, but he is the least safe of the three mids. He has no dash, and his stun is very easy to avoid.
Azir has the most poke, he can push melee champions out of lane without using much mana. He also has the highest dps. However, his main defensive tool, his ult, does not block zed's shadows, so this should not be a hard matchup. Azir also needs 2 items to actually do burst damage, so this should be a very easy matchup if you can avoid getting poked out eary game and farm with shruikens. Then when you are ready to go all in he stands no chance (unless he has at least zhonyas and nashors). His dash does mean he can get away if he's good though. Edit: I forgot you were trying to play one not against them my bad. I would recomend oriana. Azir has been nerfed a lot and is hard to play and therefore he has a low winrate outside of very high elos. Viktor is a solid choice, but oriana is safer to blind pick and has more tools to help her team with her speedboost/slow, shield, and the cc of her ult. She also has great lategame dps since her autos have an ap ratio and the cooldown of her q is only 1.8 seconds with max cdr. If you have an engage champion on your team like malphite, she makes the teamfight super easy since you just put the ball on him, r w after he ults, q then move the ball back to shield one of your carries and keep casting q as you move.

Azir is the strongest but hardest to master

I feel like is one of the best, thanks to his true damage and all AoE skills it can be pretty easy to carry games when you're fed. And like Zed, you win lane as soon as you hit level 6 most of the time. This guy carried me from bronze 4 at the start of the season to Gold. My favorite build:

Oriana: Probably the most reliable pick, ori is seldom nerfed and IMO in a good place so you don't have to worry about your champ getting gutted. Has decent zoning, good burst, lategame and wombo combo / teamfight potential with her ultimate

Azir: Was a lot better before they nerfed him, has the best zoning out of them with ultimate, Highest sustained damage out of them. Probably the safest with best mobility but scales slightly worse than oriana if you are just farming

Viktor: Probably has the most 'control' out of all of them , can full clear backline really early. Very high burst but can't fall behind in late without taking a large penalty in damage. Worst zoning but still very good with W

I'd recommend his Q and E late game deal crazy amounts of damage, and he's guaranteed to get a few off in a team fight with his passive, plus at your Elo a lot of people will QQ because of his ult, so you have the psychological factor

take for lane, play safe and focus on farm as your goal is to get to late game with a lot of items, use TP to get back to lane for farm after dieing or backing for an item. build and some AP items are all good items, as for defence, you can get away in most situations with not even building a defensive item.

He can also jungle if you know how to clear on him.

If you plan to spam the living hell out of one of them I'd say Azir. An Azir who plays above his level can take over games easily.