I think it is hard to decide.
Ben's main motivation was to make money off of Wayne's World and getting in Cassandra's pants. He was very charming to everyone at first. It was only at the end that everyone figured his plans.
Bobby only seemed charming to Cassandra. and most of his motives was simply to make the most money for Mr. Big by getting rid of all the dead weight from Cassandra, which included her band and Wayne. If he was also just wanting to get in her pants the wedding scene didn't make as much sense.
I was under the impression Casandra wouldn't lose her Visa unless she was not successful in her music career.
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Bobby has a creepier vibe, but Benjamin is a better character. If that makes sense.
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Bobby, hands down. Although, that probably has most to do with Walken's creepy factor. lol
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Bobby for sure and being played by Christopher Walken doesn't help Ben's chances of being considered a better bad guy, plus he had straightened out in the end. Just like the Rocky series where every sequel pushed the envelope with the villain and made him look more brutal.

Bobby

I have to say Bobby because the end of the 1st movie softens Benjamin up and doesn't make him look like that bad of a guy. We can at the very least say he had learned the error of his ways. Bobby is just as bad at the end of the 2nd movie as he was throughout the whole thing. A true villian never tries to turn himself into a good guy.

Ben, as Walken didn't get much to do in the sequel that was funny. And it grated that they decided to revisit the Wayne jealousy plotline again.

Those two men wanted Cassandra for themselves.

Definitely Bobby. Ben was more of a friendly rival-cum-antagonist than a bad guy.

I personally thought Ben was more of a womanizing sleazebag than a really bad guy, Bobby seemed to have more substance as the villian than Ben

Definitely Bobby. It also helps to be played by Christopher Walken.

Bobby. Ben was rather misunderstood to me. Well, he did ruin the show and all that, but he was really just doing his job. Bobby was a true a*hole.
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Bobby.
Christopher Walken is more bad ass than Rob Lowe ever tried to be.

I'm a Rob Lowe fan and he did play a great villin in the first movie but any good sequel is going to up the ante for the characters. So that being said I have to go with Bobby simply because he was a more wiley adversary. Also, you can go wrong with Christopher (I need more cow bell) Walkin.

Definately Bobby.

Well dude, come on, Bobby. Christopher Walken, just a natural born Bad Ass.

I thought Ben was kind of a weak villian and I'm glad he was able to change for the better at the end.

Bobby, definitely