In reply to Lauren_S:
I've used a variety over the years, from about 1993 onwards.
Personally I have found that polar are very good hrms, but weaker if you want speed and distance as well. they are heavier, more expensive and have only. Just started doing integrated systems. The rcx3 is interesting, but I use an rcx5 with foot pod and cycle monitors rather than gps.
Garmin are goodish at speed and distance, but have problems with software and the soft hrm strap is just plain awful. It suffers from more spikes and drop outs than polar. This is true of most ant+ straps.
Suunto are similar to Garmin, with fewer software problems , but a bit more idiosyncratic .
Timex make great watches , and if you want a sports watch that does hr as well, they seem like a good option. And they have moved of to ant system I'd not buy one...
Hard straps are less comfy, but generally more reliables.
Gps is generally more accurate for distance measurements than footpads, but much less responsive in terms of on the fly pace info. Footpods are quicker to get going in that just turn the watch on and start running. No faffing with obtaining satellites . I used gps, I then switched to Garmin Footpods , which was really good,and now use polar Footpods system. Others prefer the gps system . I can't see any major advantage to them myself apart from mapping, which I personally am not interested in for running...
I now use polar again after a break of about 8 years where I dalliances with timex, Suunto and Garmin. I really do prefer the polar reliability of data and though you pay more , and in some cases quite a lot more for what seems like little additional functionality, if you want that data, you want the data and polar gives that too me more often .
Oh, and most that estimate calorie count tend to be very optimistic ...