First off, I don't think I've ever had a BAD blow job...just some are better than others...lol.
Not that I've had hundreds of bjs from females but I can say that only 2 would make my top 10 best, and they would be in the 6-10 group.
I feel I give an amazing blow job...based on feedback. Or maybe they were just horny?? So I'd say, by my experience, men are the best at oral sex.