I've been using heart rate monitors on the bike for years. Most of that time I was using the entry level plastic strap version that came with my Garmin 305. Prior to that I used the entry level Polar HRM. These two were nearly indestructible and worked most of the time and just needed a CR2032 battery replaced every year or so.
One day I though I would treat myself, and bought the Garmin Premium Soft Strap. It was, as advertized, much more comfortable. However, after about a month, it started cutting out mid-ride. Heart rate readings got progressively worse and worse. I changed the battery and followed all the suggestions in the garmin heart rate monitor troubleshooting guide, with no luck.
I was convinced the electronics failed, so I replaced it with another identical soft strap. It worked for a month before it too succumbed to the same symptoms: cutting out and giving false reading after progressively shorter intervals. My next step was to take DC Rainmaker's advice and use a Polar strap with the Garmin monitor. This worked great for about 3 months and then it too started cutting out. It would consistently cut out on long descents if the strap dried out at all, never reestablishing a connection.
At this point, I gave up on using a heart rate monitor at all and kissed my Strava Suffer Scores goodbye. I just didn't want to go back to the hard plastic "cheap" heart rate strap, even if it did just *work*.
I saw a couple positive reviews of the Wahoo TICKR Heart Rate Monitor so I decided to give heart rate monitors one last try. The Wahoo TICKR has been working great for three months without even a hiccup. This model supports both ANT+ and Bluetooth, so it works with both my iPhone and my Garmin 510.
I'll post a followup if I have any problems.