topscore. the three topscore tests are more like the real thing than achiever, which is much harder than necessary and might cut your confidence down before the test, which you don't want. so take a test, go over what you got wrong, take some time to build up your studying on areas you're weak on, take another test, repeat. good luck next week!
I'm glad you asked that question! I've really been wondering it also. I went ahead and bought Achiever though, I have a marginal amount of time until the test date - tough doesn't always mean bad right?
I decided to buy Achiever too after looking at some old threads where people were talking about the fact that people had some sort of similar questions on real DAT... but other than that,,, it might be useless. I just wanted some more practice as well