Go to both interviews, that will help you make your mind up. You might get a job with both - or maybe just with one so the problem will be solved.
I was in a similar position in 2003 when I got offered a job at BA and VS at the same time. The interview at BA was more challenging, people were so professional and the atmosphere was so good (as opposed to feeling we were treated a bit like kids during the VS one) that I had no doubt and accepted the job with BA without any doubts after that.
All I can say few years down the line is that I do not regret my choice at all.
Good luck
FBW
