Satnav/gps devices are very good for fixed cameras, not so good for mobile cameras - the POIs show mobile sites that are frequently used, not ones that are only used occasionally.
Detectors are very good for all active cameras, including mobiles. They can be iffy with manned police speedguns, as you don't get much advanced warning - they are only detected when the operator presses the trigger. If you're the only one on the road, you'll get no warning at all.
I've been using a Snooper detector for 4 years, and haven't been caught unawares so far. I've recently bought a TomTom 510, and added the pocketgps camera POI. The TomTom gives me an advanced warning (you can set the warning distance yourself), while the Snooper warns me if the camera is active. The TomTom also tells you what the limit is for the camera.
The only negative thing about the Snooper is the amount of false alarms, from traffic light sensors and supermarket security loops.
Some of the current "detectors" are just gps based devices, that use the same method as satnav - a POI file. These seem pretty pointless - get a satnav instead.
Some are just laser and radar detectors - they beep when they detect a camera, but don't tell you the distance or speed limit.
Some use GPS and a laser/radar detector. These are expensive.
I'll keep using my satnav and my laser/radar detector, as I reckon it offers the maximum protection.