I think that Jiho Oh and Sungsoo Kim would be the most successful and also most attractive. I like their clothing choices, they seem like they would fit in with american culture. Plus Sungsoo Kim looks a little silly (in a good way, I like silly guys) in some of his pictures, like he'd probably make me laugh. I think that Jisub So would have the hardest time. I think I was turned off by some of his clothes that he was wearing and his long hair. I'm not a big fan of guys with long hair.
But I will tell you this. I had a fling with a guy from Korea last year. We worked together at an investment firm. He went to an ivy league school, was a math major (yes I guess you could call him a math geek), but he also had great style and was really nice. He was one of the smartest and hardest working guys in the office and I found that to be very sexy. I was sad when he moved to Germany. Anyways, good luck with the girl and roll model search. I'm sure you'll meet someone amazing!
Alright,I'm Canadian (Native and Scottish) and I find Korean men absolutely stunning. I think they have a more manly air to them the Japanese or Taiwanese no offense! I love them all!
Gong Yoo: I have seen him in a show called Coffee Prince and although those pictures don't do him justice he is amazing looking; he grows on you aha.
Insung Jo: He's very cute :3
Jiho Oh: So handsome and civilized when he wears his glasses!
Giwoo Lee: Looks even better with lengthily hair
Sungsoo Kim: He's alright, I'm not one for facial hair.
I think if any of them came to Hollywood if none could accept them because of there looks they would definitely win people over with their amazing acting skills. So out of them all I found Gong Yoo more attractive.
Although all of them are stunning I prefer Junsu Kim from DBSK, Bi-rain, Li Jun Ki, and Lee Dong Wook but your choices are good too.
I couldn't finish my answer in my other comment.. so I started a new one. I think that the american public would just have to get used to seeing more asian faces in mainstream movies, but that the transition could be done.. I LOVED Herold and Kumar. Both actors were hot and asian and very funny. Kal Penn is the more famous actor right now because he's also on House, so I think he would have an easier transition. But if they ever put him in a romantic comedy I would definitely go see the movie. He's very cute and I bet the movie would be hilarious.