I have a Fenix 3 and had a Ambit 2s. Ugh is all I can say.
Fenix, better all around watch ( Ambit was too big to wear day in and day out with the bump on the band for the GPS).
But the Ambit 2 for me worked a lot better ‘in-sport’ then this Fenix thing.
I have spent a TON of time figuring out my Fenix and its related issues and my main problem is the run Pace is way way off. (Yes I know all GPS watches are off a bit) but my Ambit was great at holding a signal and being consistent. The Fenix is great at being inconsistent and bouncing around. Garmin is sending me a foot pod later this week, but just seems sill to need that for the pace to work.
I like the notification on my Fenix (when I get mail and text messages) and the screen is better then the ambit.
So its a mixed bag, everyday watch, the Fenix. If you run a lot, I liked my Suunto Ambit 2S better. Clear as mud.