By piece I'm going to assume you mean trade piece and if thats the case by far big AL.
Sully is skilled, but hes limited by his size and athleticism, he has a defined ceiling.
In big AL many gm's saw huge potential which he never truly met. However, at the time he was a very attractive prospect with a lot of value.
I wouldn't say "by far" but I do think that many people saw Big Al as a possible multi-time All-Star while Sully does not seem to have the same perceived ceiling. I'm not sure why, to be honest.
Also, while Sully appears healthy now I would guess that his back issues are still a damper on his trade value.
I disagree, I say mostly everyone can agree that Sully's ceiling is david west, make a couple all star teams at best and be a really reliable rebounding big with a nice mid range game.
I'm willing to bet some GM's looked at big AL and thought
" theres my 20-10 big man, we can coach him up, better shot selection, play more D and he could be a franchise guy."
Which is why he was traded for KG, could picks and sully get us a similar type player? I'd say no.