Ask HN: How do I gracefully accept one offer over another within the same company?

I happen to have two teams within the same software company making me offers for a summer internship, and the company has asked me to to choose which team I would like a formal offer from. The teams do reasonably similar things, and I think they actually interact on occasion, despite the fact that this is a pretty large company. This means that A) I can't really make a decision based on the actual work, since it's pretty similar; and B) I may end up interacting with the team I decline.

I think I know which team I'm going to go with. One of the teams' managers got in touch with me right away, he seems to have a good attitude and sense of humor, and he put me in touch with a former intern who sent me a long and extremely positive e-mail about the team. The other team's manager didn't get in touch with me for a couple days, and when he did I just didn't get the impression that he was excited about his work. He didn't seem like he'd be as pleasant a boss as the first team's manager.

So my question is this: How do I present what is basically a personal decsion without it seeming...well, personal?