try www.radartest.com You can figure out which is the best for your money.
there are a bunch of other sites and places that test detectors but cant think of them.
radartest will also explain how radar and laser work and all that stuff. there is a lot of good info there.
I just ordered my Escort Passport 8500 Monday...wooHOOOO
I got it from www.RadarSource.com because if any store sells a Escort Passport for less then $299 it voids the warrenty and but at radarsource the give free shipping and of course no tax online.

If I were you I would just pay for half youself then you can spend 300 instead of $150, but I know that is easier said then done.