Man, I was just talking about this last night. I take class at both IO and the Groundlings. And, I can't understand when anyone uses the term "politics." There is a long wait between Level 2 and Level 3 at Groundlings. Also, you have to be passed up to the next level by your instructor. I don't know if I call that politics, it's just their way of running their school. I have gotten along with all my teachers and I was held back on one occassion thus far. It was the right choice.
Then, the other day I was taking a long-form class at a small theater in Santa Monica and some girl started talking about the "politics" that are so prevelant at IO West. She started talking about some Chicago/LA rift. I don't know, maybe I'm not far enough along, but everyone I've met at IO is awesome. Very welcoming. I think it's just different strokes for different folks.
Groundlings stresses Who, What, Where to initiate scenes. IO stresses relationship. I'm really happy with the track I took. Level 1 is almost Spolinesque at Groundlings putting the focus on the game. I feel that is neglected at IO. IO strives to make character connections that can hold up over the long-haul. I feel that is neglected at Groundlings. I'd say, go see shows everywhere you can. Find the ones that speak to you and take that path (kind of Amy Poehler's advice from the forum). Either way you go, don't think about being famous and you'll learn more.