I can't speak for everyone, but I tend to vote for the team based on a combination of who I think has the best team, and to a lesser extent witty banter. Which is why I highly encourage folks to advertise and banter for their team-convince folks why X team is the best. Sometimes I might be stuck between two great teams-in such cases, I tend to go for which team had better banter.
Sometimes I vote for the team I'm on, sometimes I don't. I don't think it's right to forbid folks from voting for their own team, especially if they truly think their team is the best. I once thought that maybe folks could have 2 votes, and vote for their top 2 teams. That way, even if you are biased towards your own team, you can still vote for another. But then folks might just use only 1 vote for their team, and that unbalances things.
Sadly, unless we do a contest to test which team really is the best, voting will always have some flaws in it.
Edit-and in this draft, I can safely say that I had a hard time deciding who to vote for. Everyone had great teams. I really mean it when I say I'd hate to fight any of them for a port

Edit 2-oh and I also factor in Blurbs when deciding. Forgot to mention that. A good team, a good Blurb, and witty banter are big factors in my opinion. Just having a great team, might not be enough.