I've sold my fenix 3 for the Apple Watch Series 2 after having used it every day for nearly 1.5 years. Running at least 3 times per week and going 2-3 times to gym, it always was a good companion, though missing some functions that were more important for me than all the metrics it delivers.
The following points made me decide for the AW S2:
1. Instant pace using just the fenix' GPS was extremely bad, nearly useless running under some trees. The instant pace was only accurate running over fields. I've tried all possible configuration settings concerning GPS, but it was always too bad to use it for serious pace-training. Instant pace for me is more important than metrics like "vertical movement" etc., which I don't need as a more or less experienced runner.
2. Tracking sports like training in gym is possible, but it lacks the option to save training plans for individual sets on the single weight lifting devices. I know, this is not, what fenix 3 was made for, but I'm looking forward that my new AW can store my training plans including weights, sets, etc..
3. Fenix 3 doesn't have the possibility to store and play music, meaning I always needed to carry my iPod nano with me. AW + Bluetooth earphones ➙ no external device needed.
4. Fenix' interface is very slow and can't be compared to the AW's
5. Optical HR monitor on the AW seems to work better than the fenix 3 HR's one. At least that's what can be read out of the fenix 3 forums and the AW tests. The fact, that I've had the device without optical heart rate, made the switch to AW even easier
Will buy an additional heart rate strap from Polar which will also work with the threadmills etc. in gym (which didn't with Garmin's straps)
6. Smartwatch functions are rudimental, meaning you can't interact with messages etc., just read them
What made me think of sticking to Fenix 3:
1. It's an extremely solid device concerning the case. I've smashed several times a squash racket on it without leaving any kind of scratches or something like that. So I've never been scared of braking it, what ever I've done
2. The battery life is much better than the AW's. This was always perfect if I went hiking. But in combination of the AW S2 and the iPhone's GPS (got my iPhone always with me when hiking in case of an emergency or something) I'm looking forward that the battery of AW S2 will be good enough to last for the day. Over night I'm going to load it using a powerbank
3. Fenix was made for sports, so this is, what it's good at: metrics, metrics, metrics. Do I need all those metrics? For me the answer was definetely "no". The mean metrics I need are the HR (which will be acquired by the AW as well) and a GPS giving me a reliable instant pace. And that's the point! Fenix failed in delivering one of those for me important metrics, meaning it lacked a reliable instant pace (even thought the track in garmin connect looked pretty spot on after the workout). This made me angry from the first minute.
I was sticking to fenix 3 for 1.5 years, because there was no real alternative for me (every other sports computer was lacking one or more functions, e.g. vibration alert, swimming compatibility).
After I've heared that the new AW would offer GPS, swimming compatibility and all its smartwatch features it always had, I knew I'd sell the fenix for this, and so i did