I have owned every possible device out there . . . Timex Bodylink, Polar 625x, Polar 200sd, and Garmin 305. I currenlty own the Garmin 305. It is best for me all things considered. The higher end polar gear is great too - 625x and the newer 700 and 800 series stuff. The Rs200sd was a flawed design and it locks up a lot. I hated it.
Toss the Timex out . . . just not in the same league with the others. It is an afterthought for them and way too cumbersome . . . watch on wrist, heavy GPS on arm, data recorder on shorts. And it is not integrated . . . as in you have to start and stop the data collector independantly of the watch. It is junk.
Modern GPS (polar 205 and 305) is acurrate and works nearly all the time. The polar footpod (same tech as the Nike and Suunto footpods) works great, but you have to calibrate it to a shoe (very easy). The polar is just start and go, the GPS you have to let it find the birds.
Garmin 10x and 201 series are junk as well . . . they have not got the GPS stuff worked out well enough yet.
GPS in the 305 is very accurate for distance, but its real time pace is not great. Polar is the best at real time pace. Great in fact.