I've broken 2 of the Garmin premium straps within 6 months. I'm not sure why they were so fragile, especially since I was careful to clean them as directed.
In any event, you can use any ANT+ heart rate sensor with your Garmin computer, so I'm using the sensor that came with my PowerTap. It's a hard strap, but it's actually more comfortable for me than the soft Garmin strap, for whatever reason.
http://bit.ly/hNMsZX
The ANT+ technology uses 2.4 GHz frequencies for transmission, and that's just prone to interference with static electricity and lack of humidity.
The best heart rate sensor I've used, as far as comfort and zero issues with interference, was the coded sensor that came with my Polar S725X years ago. Whatever wireless frequency it was using was a good choice, as it even worked in the pool, which the ANT+ ones don't.