first of all, I think it's funny when people write "best big man of this generation"..sorry, but it's clearly, BEST PLAYER of this generation..Kobe doesn't come anywhere near Shaq and Timmy in terms of impact in this generation..
as for the question..
in his prime, I'd take Shaq..there aren't many guys better than a peak Shaq, possibly nobody..
for the long run, I go with Tim..he's going to last longer as an impact player, he has half the ego, he's much better defensively, much more committed, more loyal..