I would also like for this team to make one more film and somehow conclude the story with it. I would go for the Sinister Six. That way Raimi would be able to include all the classic villains he adores like Mysterio, Electro, Vulture, Scorpion, Kraven, Chameleon -Yes! I wouldn't like Octopus to return, he had his movie and he was brilliantly done and in the end he made a choice. For the Sandman I wouldn't also hope for a return, but even if it happens I want him to help Spider-Man from the rest in the end. Ok, I know it is not like in the comics, but the films have already established their own atmosphere and characters that must be honored. For the Sinister Six to appear in a film the only logical story would be if Spider-Man is framed (by Chameleon and Mysterio). All that would be a set-up for the creation of a team with one purpose: to defeat Spider-Man. I would like this to happen, because for three movies Spider-Man is worshiped by the people of New York and it will be a real challenge for him if he would be persecuted by them. This movie would be about 3 hours long and Sinister Six would be treated as a team, not as sole enemies who team-up in the end. They wouldn't even be as powerful as the enemies Spider-Man fought in the past. So, I think this works for a film.
If the film succeeds they can always return and do 2 more with the Lizard, Venom and Carnage; the Hobgoblin and of course the Green Goblin.