I really like both guys but feel that eventually one will have to go as they are redundant. That said, if Baby can lose some weight and add a bit of vertical in his game while maintaining his lower body strength, he is the guy that will need to be kept since he is a better passer, has better hands, and is physical enough to play at the 5 position as well.
I do believe that the person that decides who the Celtics keep will be Big Baby. If he can't convert his body into some semblance of a professional athlete's(strong men competitiors, sumo wrestlers and offensive linemen aside) body, the C's will send him packing. If he does then I believe they will try to maximize what they get in trade for Powe.
Also, zerophase, I think you are being pretty harsh on Davis, especially on the point where Powe is even a better human being than Davis. Powe is an upstanding guy, but I have never seen anything written that states that Davis is not. I don't think that is very fair to make judgements on Davis' character based on what we have seen of the man publically.
Lastly, Davis had a bunch of high quality games last year and, yes, that Pistons game was one. In fact given the atmosphere in the game and quality of opponent, it could be said that in the year and a half that Powe had been in the league up to that point, he had never had a game as good as that game that Baby had. I would also go so far as to say that the amount of quality games that Baby provided a championship team last year as a tenth player far outnumbered the amount of quality games that Powe provided the 2nd worst team in the league as a tenth player.