I really haven't ever found any major differences between the major rental car companies. I think I've used Thrifty once, but I can't say for certain. I can tell you that if I was shopping for a rental car and they offered the best price, I would probably use them.

I have not heard of economybookings. That doesn't mean they aren't legit, its just that I don't remember anyone else on this forum saying they've used them.