It depends what you're after. In the UK, gatso's are radar and mobile speed traps are laser.
You're 'do everything' detector would be gps/radar and laser. Snooper and road angel are leading in the area so check out their kit. You will get a LOT of false radar though as shops use it for door openers etc, traffic lights use it to detect cars.
A laser speed reading is detected within about 1s so unless you happen to catch a bit of laser radiation which can pinged off another car, by the time you get an alert, you've been caught.
Overall, unless you regularly speed in 30 limits (!!) where mobile speed traps are common, a GPS detection system (or simply a file added to a tom Tom with the updated locations- costs £10) will suffice.
For what is worth, good observation/ driver training is far better option. Then you'll be looking out for the dangers/ hazards and you'll spot the mobile speed traps a mile off