If you’re in the Apple Ecosystem, it’ll be the Apple Watch hands down.
Discussion
I would definitely rate this under the category "privacy nightmare" even though they might be super awesome. I'd still have to trust Apple to keep their word and not just that, i additionally habe to trust in their security never being compromised.
In which case would you not have to trust the provider (just for informational purposes)?
There are a very minor amount of open source services that you can run yourself on a server in your basement. I'm sure they do nothing like Apple will do for you with fancy dashboards and stats but they can collect the data you create.
Here' a bunch of them (pardon the reddit link): https://old.reddit.com/r/selfhosted/comments/14wxful/open_source_fitness_tracker_w_self_hosted_fitness/juswr05/
Thanks man, will look into this