Teemo - Not garbage at all, not "top tier" but has some great use in a team. I build AS/AP Hybrid, almost never get my team ganked with mushrooms. Great harass with the poison, can run all over the place. I'd say second tier.
Caitlyn - Great support with traps, like teemo keeps team from getting ganks. The traps can also secure team kills by not allowing anyone to run away. I've had great success with her, always build a wriggles though. Farm and kite. Second tier also.
Tiers are very hard in 3v3 since its about team comp most the time. Having a good 1v1 champ helps, but mid to late game it is about team fights.