I have a 625 but sell both.
Polar, more useful features, HR features far superior to Timex (but for most people way overkill), more programmable workout settings (again with the overkill), Altitude which is really cool, temp which is cool but usually inaccurate, nice big display is easy to read and very customizable, Bike features are very very very useful and downloading is a cinch. The run pod is pretty accurate, not spot on 100% but closer than I would have guessed. The Polar also has hands down, no argueing about this the best new chest strap in the industry. NIght and day ahead of the rest. Plus a killer 2 year warrantee. Compatible with most gym equipment.
Downsides: Polars aren’t all that great looking, everyone has one, prone to water leakage (well the S720, 625 models at least), Price…
Timex: much nicer watch and easier to learn setup, GPS is more accurate than the Polar unit IF and only IF you get clear GPS reception. New GPS shipping now is even tinier than the old unit. New unit is shiny black and not the rounded “8” shape, smaller and I think it says GPS in big letters along the bottom. Well basically the Timex is cool because it’s a timex and it just looks better, fits on your wrist better and Timex has thier shit down in ease of use. Plus when the GPS is working well it’s really working well and you can use that very cool motionbased website Tom talked about.
Downsides: GPS is spotty man a time, not the best warratee and they take FOREVER to come back, think POlar takes a while try Timex. Chest strap often breaks and they don’t sell replacements, GPS eats batteries to fast for bike use, big chest strap, only one size in chestrap. You have to buy a seperate download kit for $70 and it’s one more piece to carry so that’s the watch, chest strap, GPS unit and a download kit. That’s two things on your waist band, the Polar is much more transparent.
The lower level Timex HR monitors kill Polars offerings on price style and are on par with performance. If you are comparing just the speed and distance capabilities for running they they are pretty even. But add in Polars biking features, advanced heartrate settings, better downloading… they are overall a much better watch imho.