I have been using Garmin for the last 6 years or so starting with the Garmin 310 xt and now the 910 xt. Before Garmin I was a Polar user for many year but when Garmin came out with the integrated GPS and heart rate monitor I was sold. Polar had their GPS arm pods which were bulky and awkward at best while Garmin even though it was a relatively large wrist unit it was fully integrated and could be paired with other 3rd party devices using the ANT+ technologies unlike polar.
I really like Garmin and recommend it to a lot of the athletes I work with because it is so user friendly. However, there is one issue with Garmin that is really frustrating. You only seem to get ~ 8-12 months out of a Garmin soft heart rate strap before it starts to throw out random heart rate readings or it just stops working all together. It does not appear to matter if you change the battery, these problems continue to persist until you get a new strap which is a real pain and a significant cost. It is not just me who seems to be having these problems, a large number of athletes I work with have had the same problem.
1) Some people have had good success from washing their heart rate strap after each use. So if you have not been doing this then this would be a good place to start in terms looking after your heart rate strap and hygiene in general.
2) A number of athletes contacted me saying that when their Garmin heart rate strap gives up the go, instead of buying a new Garmin strap they buy a cheaper 3rd party ANT+ heart rate strap. Because of this global ANT+ network you can switch in a cheaper heart rate strap and solve the problem for a fraction of the cost.
If you have had problems with your Garmin post a message below and let me know what it was.