I think for runners garmin is better, but to be honest I don't think for other activities that any fitness wearable has really shown through as being superior for heart rate monitoring other exercises such as HIIT or weight lifting.
My fitbit was particularly bad at picking up heart rate changes in T25 and insanity, but that seems to be a common complaint across the board for all current watches. The blaze is supposed to be a lot better and does have better ratings/cheaper price on amazon versus the garmin vivoactive. However I do believe the garmin has stand alone gps which makes it massively better for runners versus the blaze that still requires a connection to your phone.
To be honest I'm not sure why I want the apple watch 2 over blaze/garmin other than better water resistance/aesthetics. It really bothers me I trashed my fitbit just by accidentally jumping in a pool. I think I'm just hoping the heart rate accuracy is improved because it is newer
.