Hmmmmm. Well, the first time I saw him was in issue ASM #300... so McFarlane's original will forever be iconic. BUT, my favorite is the variant cover to Venom #19, the Venom Mary Jane by JeeHyung Lee.
I suppose it would depend on the version of Spiderman. Teenager, adult, etc. Plus, Spawn's tendency to emulate Spiderman comic covers shows that he's a seriously huge fan. So, stalemate.