I think something like Apple Watch is the way to go if you really care about real EKG. That being said the new Garmin watches seem to have EKG going on behind the hood and they are actively working on it so it may be something coming out officially in the next few months as features. Basically from what DCRainmaker had Garmin is collecting data in the background so it can be compared to the actual studied data.
If you're looking for specific features, 100% verify the watch you're looking at has those features. For instance I really like my Forerunner 245M, it does biking, screen mirrors to my Edge but it doesn't hookup to a power meter. Whatever for me but that is a dealbreaker for some people and would need to step up to a 745/945. I wouldn't be surprised if EBike features are not on the lower-end models, or maybe on a Vivo but not Forerunner, etc. Joy got the Forerunner 45 and while it's really similar to the 245 it's missing a bunch of analytics features. Would never even know they were missing if I didn't have them on my watch.
Also, whatever ecosystem you are in may play a key factor. If you like Garmin, save your stuff to Garmin, I'd say stick with them. If you don't care there's other watches out there like the Coros which have a ton of features at a great price, but could be missing some of the features you want.
REI is probably the only local store that has a good selection of the watches to try on for size. If you have huge wrists it definitely helps open up your options as the higher end watches tend to be huge.
WTF does the watch even do with an eBike?
