Brown is an inch taller, two inches longer, and a bit more explosive than Winslow. He's a less bad shooter (which is not saying much).
However, Winslow is better at everything else. He's a better passer, better feel for the game, a *much* better defender. Brown has been solid on D and there's no reason he can't be good in the NBA, but Winslow has DPOY potential, and that's where most of his value lies. Brown will never reach that level on defense, so there's way more pressure on him to be good offensively, and it makes his shooting woes more worrisome.
I still think Brown is in contention for the #3 pick, but I expected him to be a bit better than he was this season, and he's clearly a worse prospect than Winslow was.