Jax, Shaco, And mord IMO are the three most dominate 3v3 champs around. Tryn gets close to being top 3, but Jax/Shaco/Mord will single handed win a 3v3 if the person is good with them. I laugh when I see my enemies pick Ashe, TF, and some tanky dps like Sion. I laugh when I see fiddlesticks in 3v3. The game is not balanced at all in the slightest for 3v3, this needs to be remembered when you play that mode and you need to choose a champion thats suited for it.
Jax passive turns his dodge into MR for people trolling the guy saying he can't be nuked >_> When you get your dodge set up it's basically a free FoN. Building magic slayer Jax is actually a lot of fun.