I'm going to throw out some of my opinions on champions in Twisted Treeline based on my experience with it at this point.
Ban or Pick Champs
Rengar - Lots of bushes and no wards makes him hard to deal with.
Darius - Hard to kill and deals good damage with an execution ult.
Jayce - Great damage from such a tanky champ.
Singed - Very hard to kill and fling makes him able to pick ppl off.
Teemo - Shrooms for vision plus slow and poison to finish.
Jax - He jumps, he dodges, he smashes your face.
Strong Picks (Possible Bans in place of ^ those champs)
Wukong - Ability to smash face then vanish plus a knock up ult.
Garen - Spin to win and ult to kill.
Olaf - High health with a slow and some true damage.
Dr. Mundo - He isn't as strong as he was on TT but still hard to kill.
Kha'Zix - He vanishes and he deals pretty strong damage.
Cho'Gath - AP build gives him the damage he needs plus his CC.
More to Come
(Also note that 1 champ as an AP and 2 as AD seems to work best, either all very tanky or 1 that isn't. I've seen a strong early game ADC plus a tanky AP and tanky AD work very well. Also have seen a burst AP plus two tanky AD work well.)