I really like the Forerunner 220, a couple minor details why I like it. the audible beep is really loud, so when you're running with people and the lap goes off you can hear it and not miss what your mile split was. the lap button is really easy to press. you would notice this on track workouts when finishing a rep.
The GPS track is always solid. never gives me fits minus the Bluetooth needs turned off/on a lot if im going to sync an activity this method. But I usually just put it on the USB charging cradle when im at my computer.
The Forerunner 630 is a badass high end running watch, the screen is much bigger / sharper and overall nicer than the 620/220. I've noticed the lap button is a little harder to press and sometimes I find myself fumbling with the button as im crossing the line on a workout. (though ive only used it twice on workouts now vs a year +with the 220)
One con on the 630 is the audible beep is a little quieter, but that's just a petty complaint. I essentially use the same data field options as the 220 (timer / pace / distance) (lap time, lap pace, lap distance ) but you get the option to have more to choose from, back to start navigation, bike settings and some smart watch capabilities.
The new running metrics are cool when you upload them to Connect, however I don't find much use out of it.
If you need just the essential running features: time/pace/distance and do weekly workouts get the 220.
I find the Fenix 3 a fun device, however as just a runner I don't care for it. Even trail running I just end up taking the Forerunner 220 or the 630. Overall I end up just recommending the 220 to everyone I know.