To move or not to move

There is an opening at work. Not a promotion only a lateral move. The issue is that alot of the promotion comes from within this unit. So the question is do I want to stay where I am with the people I enjoy working with. A Boss who goes to the wall for you when things are tuff. Or do I want to change to a unit were I would not be on the phone all the time just 4 hours out of the day. The boss is great. The people in the new unit are cool. I have worked with them when I work over time They are professional and personable. Very helpful and I have been aproached by a couple of them to apply for the flex team. So that is were I am deciding do I stay where I am comfortable or do I make a move with possible advancement? Any suggestions?