I’ve used the Garmin Forerunner 910xt and Garmin Fenix 3. I’m going to sound like an advertisement for Garmin here but Garmin’s customer service is superb. They troubleshoot with you patiently on the phone and if you need product replacements, they are happy to do so to keep you happy. Both watches require the chest hr strap. I’ve found the wrist based hr strap to be really inaccurate. I just throw on anti chafe stuff so that the hr strap doesn’t cut into me so much. The 910xt is a much older model (read: cheapest). The Fenix 3 is a more recent model and so more expensive of the two. I’d be wary of purchasing used watches online. Garmin only provides customer service care when you’re the original buyer. Hope that was helpful!