As far as the Apple Watch's heartrate monitoring is concerned, it definitely has one. Not only that, it's significantly more accurate than any other fitness tracker's.
http://www.mdpi.com/jpm/jpm-07-00003/article_deploy/html/ima...
More precisely, according to one study, compared to other devices including Fitbit's 2014 model, Surge, Apple Watch in workout mode was found to be more accurate.
You know Apple Watch was in workout mode for the study because outside of workout mode Apple Watch only measures heart rate when you're still, according to https://support.apple.com/en-us/HT204666 ... note that in workout mode Apple Watch battery life is "up to 8 hours" according to https://www.apple.com/watch/battery.html
The study did not examine more recent Fitbit models (Blaze, Charge 2, Alta HR) and did not examine Apple Watch outside of workout mode.
Disclaimer: I work for Fitbit but don't speak for Fitbit.
"What’s notable to start with is that it took almost 2 minutes after pressing the start button for the Apple Watch to decide on a heart rate. At which point that heart rate was incorrect by 40 beats. It wasn’t until 7 minutes into the run that it agreed with everyone else."
https://www.dcrainmaker.com/2017/02/apple-watch-series2-nike...
I have no idea what I'll get when my current Pebble bites the dust. I'm not sure which is more likely: that Apple offer a watch with more than a couple days battery life, or that Fitbit actually integrate the Pebble tech (and reliability) into their devices. Sigh.
And it has an excellent heart rate monitor.
Every single model of Apple Watch since launch has shipped with the same optical HR measurement system (IIRC teardowns of gen 2 confirm this), working on largely the same principle as the optical system on the Peak watch.
I actually really liked my Peak, whose battery lasted nearly a week, and which had a reliable heart rate monitor. After the recall, I tried an Apple Watch (v1) and various other smartwatches. The Apple Watch was, for my purposes, inferior to the Peak in several ways: the battery life was very short, it had no HR monitor, and it was very expensive. In my experience, the Peak even pushed notifications from my iPhone more reliably than the Apple Watch.
To be sure, the Peak wasn't beautiful, but as a V1 it seemed like a product with legs.
disclosure: I received my Peak for free from Intel at their ICAP conference.