i have a valentine 1 for radar and a passport laser shifter for laser.
the V1 is the best radar detector IMO. laser jammers require installation, which isnt as convenient as the radar detector, but if the cops in your area use laser instead of radar, then the V1 will only let you know that you're about to get a ticket (once youve been hit, it's too late). The laser jammer will 'deflect' their signal and notify you, giving you time to slow down.
if you get hit with instant on radar, youre screwed, unless you have something illegal in your car to block it.
keep in mind, these devices are illegal in certain states (such as VA, DC, etc.)
even with these devices, though, youre best bet is probably still smart driving - knowing where and when its 'ok' to speed. depending on these devices blindly is nothing but trouble.
cheers.