There are many forms of the sinister six ranging from different characters in the comic and the cartoon. MY ideal six would be, in no particular order:
1. Green Goblin
2. Doc Occ
3. Shocker
4. Vemon
5. Mysterio (one of my favs, I mean who can't not like this guy)
6. Hydro-Man/Sandman/Electro/Vulture are interchangable