Played about 30-40 games so far and I'd say:

AP Panth- W is a 1:1 ratio, and is very close to permastun, and a gapcloser to boot. Also ult is 1:1 ratio and the amount of people that will stand in it is funny.

Irelia - Simply put with that stun, true dmg, tenacity, and how quick she can get triforce, how easy she sticks to targets with Q CD, there's really not many people that can 1v1 her, and I mean like an absolute handful.

Shen - you can play him AP, but I prefered jungling with him and building just full tank. Simply put you're practically impossible to ACTUALLY kill, regardless of how long it takes shen to kill you, it will happen eventually as he takes very little (if any dmg) due to permashield+taunt.

Vlad - need not elaborate.

Xin Zhao - Once you get just a little attack speed, that knockup is just constant, your E means it's really difficult to get away from you. Like irelia can 1v1 a shocking amount of people.

TF - His Q has a huge range, by the time you get to TF you've probably already ate 2 of them, it doesn't matter what card he picks. He is kind of weak say 1-5 but once you get some AP he just does such a huge amount of dmg that if you cannot 100-0 him instantly, you probably die trying to kill him. He also has probably the best wave clear.

Leona - build her AP or AD doesn't really matter you're naturally tanky and permastun/root. E range isn't that greate so somewhat flash reliant. People will kill themselves trying to kill you a lot though.

Sejuani - I like her, built full cinderhulk tank for just the CC spam. :)

Then there's the usual Ez/nid etc.

heres the winrate though for a general list: http://www.reddit.com/r/leagueoflegends/comments/319k2e/urf_win_rate_2015/