Okay let's say you have two AA scores and percentiles:
Student A with 24 (95%)
Student B with 21 (94%)
Obviously student B got the harder test because about the same # of test takers got his/her score or lower for that particular test. But if I were looking at the scores I think I'd notice the 24 over the 21.
Seriously, anything 21+ would be great.
And for the GPA/DAT question, I think it depends on the school you are applying to. Some schools want a higher GPA. Others look at the DAT as a good predictor of dental school performance. Figure out which one of yours is better, then figure out which schools want that one to be high. Then apply to those.
TBH I think a high DAT will give you a better edge than a high GPA, simply because enough people can get a 3.7 or higher but the DAT seems to be designed to average around a 17 with a nice spread. I got a 26 AA; had I gotten a 20, I doubt I'd have gotten into so many schools (maybe only a couple).
Had I gotten a 19 with a 3.8 instead of a 3.46, I'm sure I'd have gotten into a bunch of schools but I don't think it would have been as many.