Probably Bynum when you consider potential trading partners.
Gasol, while more valuable than Bynum as a player, is on the downside of his career and has a rather hefty contract remaining. Teams looking to start anew aren't going to be interested in him, largely because he isn't a guy you build your team around at this stage. He's a great complimentary player -- one of the best in the league -- but franchise player that is going to carry a team to a championship he is not. The teams that he would help the most would have to give up entirely too much to obtain him and that would probably set them back or at a minimum introduce too much uncertainty. For example, he'd likely make a team like OKC a serious contender and elite team, but they'd have to give up Westbrook and one of their better defensive bigs in return, at a minimum. He's be great on the Hornets as well, but we'd be interested in getting back CP3 which makes that a pointless trade for them. None of the contenders would be interested because it's just a lateral move at best.
Bynum, on the other hand, is still young and a guy that might make an excellent piece on a team looking to build around a youthful core. Perhaps he'd be a nice starting point for a team looking to rebuild entirely. I don't think teams are really looking at Bynum as a franchise player at this point, because he's entirely too injury prone and he hasn't really been able to sustain a high level of play on either end of the floor. He does have a huge expiring though (next season), and chances are that he'll have to sign for less money on a new deal so that makes him a bit more tradeable. Teams could either use him to shed serious salary or use him as a building block, so I think it goes without saying that he's more valuable as a trading piece.
Ideally, if we do end up trading Bynum, we'd have to get another reliable big back in return and address a major weakness. I can't think of a better deal than Bynum + Artest + Blake for CP3 + Okafor, but that would require a guy like CP3 to start making serious demands to get the process started. CP3 leaving the Hornets == rebuild mode and getting Okafor off the books is a must. I'm not so sure that they'd want Artest though, but the deal does get them well under the cap and they getting decent PG in return. Just a bunch of wishful thinking, of course, but that would be the deal I'd love to see.
