I'd probably want to look like Tsunami's Venom-clone (like the way Robertson looks more than Eddie), only maybe with a bright red costume (similar to Carnage's). I'd also have the whole screwed mouth thing, giant tongue and all, because I think that looks really tight.
Of course, I'd have total control over the symbiote but would use its power for both good and evil.
GOOD: Protecting the nerds at school from the jocks 🙂.
EVIL: Keeping the jocks at school in check 🙂.
Actually, I'd probably want the ability to ooze around like a puddle so I could rob a bank in order to fund my personal expenses, but then I'd go and help stop crime. Unless I didn't feel like it. Though I would go and trash the place I work because I'm pissed at it right now.
The ability to form my hands into weapons WOULD be nice, but I think that I could do without it. I would want to be able to shoot those shard things that Carnage does, though.