Depends on budget:
Garmin Vivoactive HR
Garmin Forerunner 235
Both excellent (the former does other stuff, the latter is mor running oriented)
There are (superceded) versions without optical heart rate monitoring which will be cheaper (Vivoactive and FR230) - both of which will work with an ANT+ chest strap for heart rate when it becomes necessary (it will).
Then you move up to the FR735XT and the Fenix 3 (various models with and without optical HR) and things get expensive.
I've a Fenix 3 sapphire (no HR) which is ideal for triathlon training. A colleague has the same with the HR and it looks good - the convenience of not having to remember the chest strap (and wash/clean it and replace batteries, etc.) is attractive.
I'd set a budget first and then find out exactly what it will be used for.
Then go here:
http://www.dcrainmaker.com/2015/11/w...endations.html
That will tell you what you need.
Cheers,
Mark C