I really dont have any experience with the Timex, but I love my Garmin 310XT! Does most things great and very easy to manipulate while riding or running. No HR while swimming and the GPS is irratic if its not in your swim cap but thats about where the short comings end. I have had mine for over a year and the only way I would go to something else would be the new and improved version of the 310XT if they made enough improvements!!
Hope this helped.