I don't necessarily like Travolta, but I don't hate on him like a lot do. He's ok. I liked Fraser in With Honors and School Ties. Other than that, can't think of a movie he has been in that I liked.
I agree on Travolta. Sometimes he looks awful but then he will pull off a performance that makes you like him again. He had his moments in Swordfish, and even Ladder 49 was decent. As the firechief he was believable. Some of his older stuff is his bread and butter though - Sat Night Fever, Kotter, Urban Cowboy.
All of the others that K mentioned - they are what they are. Sandler, Reynolds, Cook, Vaughn, James, Kutcher - none of them are bad if you take them at face value. If you expect an A performance out of any of them, that's when you get a letdown. They are silly actors that make slapstick movies for the most part. I don't expect anything more from any of them.
I do think that Freddie Prinze Jr, Paul Walker, Keanu Reeves and Brendan Frazier are some of the worst actors Ive ever seen.