Which preposition you use depends on your intended purpose with the sentence: If you say I belong with team 1 it refers to an association meaning that you belong alongside team 1. It gives the impression that you aren't a part of the team but are next to them. To say that I belong to team 1 gives the impression that team 1 owns you; you are a part of team 1. I belong in team 1 sounds a bit strange; I think it would sound better as I belong on team 1. This indicates that you believe you should be a part of team 1.