I'm very happy with my Garmin Epix (gen 2). It's got a nice AMOLED screen, which works better for me cause I'm honestly mostly using it indoors, and I don't really need 50 days battery life or anything like that. 13 days on pretty high settings is plenty for me...

The watch has its own built in GPS antennas, and works fine without a phone during activities, since I saw you should about GPS stuff elsewhere in the comments. I'm pretty sure it needs to sync data to a phone eventually though, for full functionally.

This is probably overkill for you, and you can get one of many much cheaper options from Garmin since all you care about is heart monitoring.

Apple watches are the only ones I know that do the full EKG thing if that's something you're interested in, as far as other options. If you already have an iPhone, I've only heard good things about the watches too. Pretty sure their adventure watch only really loses to Garmin on battery life.