That depends really. If youre driving for some two bit outfit, then yeah, I'd be real scared about being on percentage. But if it's a larger, stand up company, then it shouldn't be a problem. I understand TMC pays on percentage, and say what you want about them, but if they made a habit of ripping people off they wouldn't be as big as they are, not last as long as they have.
Per diem is also something I've worked for, and I have to say, tax free money is nice. Especially since I hve no faith whatsoever in the government to actually pay out what I'm putting into Social Security.