Top:
Poppy. Because hyper-carry top lanes are really, really strong in the 'wet noodle' meta. She is very strong against pure tanks due to %max hp damage on Q on a short cooldown, and if it turns into a farm lane she scales absurdly hard. She also has a good kit for farming under tower if she needs to and does brutal burst damage for ganks. Honorable mention is any Marksman, because they can bully melees so hard and free farm.
Mid:
Pantheon. Who bursts harder pre-6 than any of the mages that are played mid? Pantheon does. Who harasses harder? Pantheon does. Who can man-drop into any lane for a brutal gank? Pantheon. Who snowballs stupidly hard when they get fed? Pantheon. Also, he is the most manly of all champions.
Jungle:
The meta is all over the place. Ranged jungles were awesome for a bit there, but not as strong any more. Nidalee was off-meta until last week when she became FotM. I guess Cho'Gath jungle, which isn't super off meta, but is really strong. He can full clear first rotation super easy. He has strong CC and strong burst. Depending on the needs of the game he can run Magus, Juggernaut, or even Devourer. Good and tanky, good damage, Feast is amazing for securing objectives. His ganks are passable. I like him.
Marksman:
Ahri. If you haven't played AD Ahri yet, you are missing something glorious. Build her like Ezreal, Manamune-Trinity style. She lacks AD ratios, yeah, but look at her kit... Q is now a huge movespeed buff which is always amazing on Marksmen, it has true damage to help make up for the lack of scaling early game, and gives her great early to mid game wave clear. W is a one point wonder: It is cheap to cast, and procs Muramana THREE TIMES because each Foxfire is counted as a single target spell. E is a long range long duration crowd control spell, which is unheard of on a Marksman and it procs Muramana. R is obviously super strong on a Marksman, because hyper-mobility is the most OP thing possible on a marksman. Add to that her passive, which gives her lane sustain and the new changes to up all her base damages and you have a brutally strong marksman.
Support:
Gangplank. But only in an AD heavy or auto attack heavy composition. E max and rush a Zekes. 25 minute team fight? E+Zekes gives everyone on your team: 40 AD, 10% movespeed, 10% Lifesteal. To put that into perspective, lets look at gold value numbers: Only counting the stats you give to your allies, not including stats given to yourself, those two items combine to give your four team mates a total of: 5760 gold worth of attack damage, 2200 gold worth of Lifesteal, and 1580 worth of %movespeed. So, on just your allies you are adding 9540 gold worth of stats. You know what a 9540 gold advantage looks like in a team fight? Yeah, exactly.