This is from a gal's POV about the guys of these species
Klingons pluses: Wouldn't think you're unladylike for liking Bloodwine. Minuses: Probably don't use deodorant, won't pick up their underwear, and they may love you but, you may not survive an encounter. Another plus they won't leave the cap off the toothpaste(oh they don't use toothpaste...). You'd have to learn how to cook heart of Targ.
Romulans: They probably do use deodorant, pick up their underwear and wouldn't get on you for your lack of cooking skills(Romulan Cuisine doesn't have a great reputation). Unlike Vulcan men, they won't discuss Quantum physics. Minuses: They probably would be tyrannical and control freaks. They would probably brook no argument and don't even ask what they're thinking or where they've been. As for an encounter, you'd have to stay away from the extreme kind who'd say "YOU ARE MY PRISONER!!!" in the sack. Any Christine Chapel type would not suffer unrequited love from these guys.
I'm basing my guesses and opinions TOS, TNG, and DS9 episodes featuring Romulans an Klingons. On balance who's sexier it depends.