Together is more fun, for sure, particularly if you want to take down a strong gym. It's great to know who plays in your area too - I know a few people and we sometimes come up with a bit of a strategy (nothing too serious though).
Such a shame you need to choose the team so early in the game, I'd much prefer to choose the same team as my friends, but it's too late now.
I'm Team Instinct. And you?