Google Fit would probably be the smartest choice, because it has support for different hardware vendors. For example, Withings has Google Fit integration so you'd get their range for free.
Ups for google fit. I can tie my Pebble into that (at the moment), so it'd give me a leg up.
So to speak.
I didnt like the API compared to other vendors. It was quite basic and a much lower level. The plus side is vendor support