for the most part the practice tests are harder than the real thing, but thats mostly because they ask wayyyyyyyy more obscure and detailed questions than anything you'll find on the real deal. main difference? the real deal has much more broad questions, so you're best bet is to study broadly, know your basics, and not freak out over practice test scores.
generally....
Achiever :
effin hard. RC and QR are pretty close to the real deal though, as are PAT angles (angles on real deal are much harder)
Topscore:
Much closer to the real test, especially the PAT (except for the angles). RC is more inference based on the real deal though, so beware
Kaplan:
sciences and math are tough on Kaplan, whereas kaplan PAT is a JOKE! joke...joke...joke. your score will def go down from whatever you get on kaplan PAT bc its way too easy. once again, RC is more inference based on the real deal than kaplan, so keep that in mind.
use the practice tests to motivate you to score better, but don't give up hope.
best of luck
