1. Venom- Now obviously all characters revolve around who and how someone is writing them, so my reasoning is essence I get compared to others. Brock, despite those who think his reasons for hating spiderman are pointless or vague or that he brought it on himself, or whatever...bottom line being he does blame him. Don't care if you like why, but Brock sees Spiderman as a problem and tries to eliminate him. He fights spiderman just as hard as Spiderman does other villians, because he perceives Spiderman as a villian, someone who destroyed his life. He isn't fighting for power or money, he is fighting Spiderman because of an injustice he feels. I think anyone can relate to feeling like someone else has short changed you some how. Add the symbiote making him a little wonky in the head, and his desire to not fully be taken over by it, and I think you have a character that should be appreciated for more then vapid brute. Theres more to Brock then I think people give him credit for. That's my opinion.
2. Lizard- Granted, Connors did it to himself, but how horrible is it for your mentor/professor to turn into a monster he cannot control. I think the duality of this is character is really tremendous and I have loved not only the comics, but how both the 90s TAS and the S-SM have portrayed him.
3. Mysterio- I actually do not know why I like Beck so much, maybe it's the fishbowl. But I think he is underrated, and would make an awesome villian visually in the movieverse.
4. Carnage- I've once read that he is intended to be like Spiderman's Joker. A sadistic mad man. In the DC/Marvel cross over (if someone can tell me what the issue was I'd be thrilled) several years back, Carnage even sought Joker out. I agree with many that he isn't the deepest character, but he doesn't need to be. His insanity mixed with his power makes him so dangerous. The sheer joy he gets in murder is sick without a doubt, but like he's said, "Anyone can kill, if you only have the courage." (That quote I don't think was verbatim)
5. Hobgoblin (Jason Macendale)- I think someone else in the topic said it best, he is a great display of greed, criminality, and corruption. Do I think he is better then Norman? No, not really. Do I like him better? Yes, I really do. I think he can be underrated at times, and I cannot wait to see how S-SM portrays this Criminal Mastermind.