There are two which are Known as the "best".
Valentine 1 - one of the major things the V1 has which others don't are arrows that show you where the radar is coming from which in my eyes is useless because if a radar is coming in, I don't give a shit what direction it's coming from, I'm going to be cautious regardless. The V1 also has a lot of false alarms.
Passport 9500 - is the other "best" detector. It has built in GPS which learns false alarms at specific locations and stops giving false alarms (which is a huge feature) and it has a database of red light cameras. Because it has GPS, you can even mute out your own false alarms by hitting mute 3 times so it stops bothering you I the future ONLY IF IT'S THE SAME SIGNAL AT THE SAME LOCATION. If a new signal is present is at the same location where a false signal is marked, it will still tell you.
Escort, the company that makes the Passport, just released a very new feature called Escort Live. It's a special wire for your detector which syncs with your iPhone or Android over Bluetooth. The point of Escort Live is to use other radar detectors owners detections and signals in your area to show you way ahead of time where a speed trap, laser, or live radar unit may be so you are careful. Obviously Live will need a healthy amount of users to work well, but it is a brilliant approach to radar detections. Escort Live, along with all the other GPS features of 9500 is what sold me on it and I just got my Live Cabel on Friday.
Hope this helps. You may also try some radar forums for comprehensive comparisons of 9500 vs V1.