I'd like to keep both but if we have to sell one I'd much rather sell Ozil than Alexis for a couple reasons.
Ozil is a brilliant player but he needs the team built around him in a certain way to get the best out of him. Alexis, in contrast, could succeed in just about any team. There is no team or setup into which a versatile forward with exceptional goal scoring ability and a hard working do-or-die attitude cannot fit.
While I think Ozil has gotten far too much stick from the press and some fans during his time at Arsenal, I also just think his personality fits in a little too well in the cozy, comfortable environment that Wenger has created at Arsenal. Alexis has his own attitude problems but to change the mentality of the club we need more players like him, not fewer. We need players who are disgusted by losing and who will call out their teammates for not putting in 100% during every training and every match.