Check out the Garmin Fenix series. I can’t say enough good things about the Fenix. I wear mine EVERY SINGLE DAY and LOVE LOVE LOVE it. The Fenix 3 can be found for apretty good price because the new Fenix 5 is out.
You can pair either a Wahoo TICKR or Garmin HRM to this for heart rate (I use the Wahoo) and it automatically uploads to Garmin Connect which syncs with Strava.
Garmin Fenix = 11/10 in my book. I use it for biking, hiking, skiing, paddling, really everything!
I use a garmin vivosmart. It was a good value at the time I bought it. I would buy it again if something happens to this one. It has worked flawless for me and I like the features. I have it on most all the time. For MTB i use it as a heart rate monitor and start a new “activity” right when i get going. The “activity” keeps the heart rate in the screen so a quick glance gives me the information I want. The screen is modifiable so you can configure what you want to see on the “home” screen for the various activities. I’m not sure the accuracy but it gets me close enough to know when to back off a little or just stop and take a quick break. I’m 53 ride like I’m 25 at times and don’t need no issues with the ole ticker while out riding.
Wait a week and get the new Apple Watch. I’m still on the first gen and love it, on and off the bike. I’ve been waiting for them to bring out one with GPS and LTE, so finally the phone can stay in the glove box.
I’ve got a Garmin 920XT and love it. It came with a chest-strap heart rate monitor, which I’ve never used, so can’t comment on that, but the watch is awesome. I wear it everyday because it also has a step counter. Battery is normally good for 2- 3 weeks between charges. It’s been abused pretty good and has a few scratches and dings, but keeps on ticking. Not sure if an apple watch would stand up to the abuse of off-road riding, the couple I’ve seen so far seem a little delicate.
You can also customize the 920XT with additional downloadable apps, watch faces, screen layouts, etc. I do wish it had a native stopwatch, but there’s an app for that.