Depends on what we want in the future.
Messi at the middle seem like perfect option for him and our midfield. It brought back the balance to midfield and we aren't vulnerable defensively anymore.
But it limits our option in attack, we have only him and Suarez when he finishes. Could it be different if Suarez start performing and Dembele is back to the team?
If this is the case I would want a guy like Martial, may be Coutinho on LW and some other signing for midfield?
If we decide for striker then we might go for Dybala if he shows he can coexist with Messi more in the NT, Icardi (although I hate him being sob) could be another option. Werner is popular here too and he is undeniably goal machine. Not sure Griezman will work well here
btw, in both cases a guy like Mpabbe would have been perfect fit,but that ship has sailed. but on the other hand many didn't know about him 12 months ago so may be someone else will come
edit: didn't refresh the page before posting. I've basically sentence look like it is copied from Devils post now