There is really no comparison between Spiller and Quiz. Spiller has elite speed and starter's size, Quiz is small and slow, and even as agile as he is, he'll need to develop elite vision to make a big impact. Spiller was a top-10 pick who has been understandably "stuck" behind a great RB in Fred Jackson. Quiz was a 5th rounder who has been unable to pass the corpse of Michael Turner, who is now so slow and so lacking in explosion that he might as well be running backwards through the hole. Spiller has proven that he can score from anywhere on the field, that he can produce with limited touches, and that he can carry the load admirably when given the chance. Quiz has done exactly nothing in the NFL.
In summary: Spiller vs. Quiz is not a fair comparison by any stretch of the imagination. Pedigree, play-making ability, and an entirely reasonable excuse for the delay in his "coming out party" vs. well...uh...Quiz has a cool name and lots of wishful-thinking hype from fantasy football owners. Oh, and all off-season his coach talked up a role for him in the offense that to this point doesn't seem to actually exist.