Despite fear of sounding unoriginal, I also have to say that Venom is my favorite Spiderman villain, and second favorite Marvel villain overall, just behind Dr. Doom.
The Lizard is a close second, and the main reason why I wanted to see the new Spiderman movie despite my dislike of reboots. Although I thought CGI effect on him was pretty bad, and it was obvious a lot of his character development and motivations were cut out of the movie, I was just happy to see him on the big screen. Especially when he finally was wearing his lab coat while fully transformed, that made me really jolly, even though it was just for a quick scene.
And to be honest I don't really have a least favorite villain. Even the super silly ones like Rhino, Mysterio, and Shocker make me laugh with their silliness, so I can't bring myself to hate them.
As for a sequel, I really want J.J. back (as long as he's still played by J.K. Simmons) and although I'm not too keen on my spiderman knowledge, if my memory serves correct I believe he has some kind of relationship with Scorpion, so maybe bring in those two together as a package.
Other than that, Venom needs his own movie to truly shine, so I'd like to see that, bonus points for Carnage.
