Faultless

I use this for basically every workout of mine, and I workout everyday. The combo of the app syncing with the HRM is beyond perfect. If your phone is just in the room and you've tapped to start your workout on the app, it will track your info. Doesn't have to be right next to you nor does your screen have to be on.
It can connect to GPS as well and track your distances/routes as well as how what your pace is.

Pairs easy and no need to buy a receiver so it saves a whole lot of money.