Any recommendations for training watches?

I have two.  A Garmin Swim 2 I use for swimming, and a Garmin Fenix 5s (?) I use for everything else.  The "multi-sport" watch won't measure heartrate while in swim mode.......which I did not know when I bought it.  It also lacks a stopwatch and a countdown timer (so if I have an interval that doesn't end in 5, like 36, 52, etc., I need a beep to say when to go).  Which is all to say that the "multi-sport" watch is pretty worthless.  But it does do stuff like track my VO2 Max, etc.  It really depends on what you are after.  I'm a swimmer who occasionally bikes or whatever else.  The cyclists who swim have a very different view than me (i.e. "if it isn't on Strava, it didn't happen").  The Swim 2 is a very useful tool to help me train.  It it not useful in broadcasting to my peer group that I worked harder than them 3 out of 7 days last week.

Can you tell I get annoyed at my tri-athlete peers who won't go if their watch isn't properly recording everything?

But seriously, if you are looking into a single device for multi-sport training, make sure that it will measure heartrate in the water.  Oh, and the calories burned algorithm is junk.  Doesn't matter if I do a fly set with my heartrate constantly exceeding my theoretical max, or if I tool around in the water, it gives me almost the exact same result per yard.  As is the yardage......any kick sets, underwater sets, or drills utilizing one arm at a time are not going to be picked up.  And the distance for open water swimming is highly suspect.  Easily 10% variable when comparing to other peers.  

Now that I think about it, the most effective watch I had was when I started a few years ago, just a Timex Ironman.  It had a stopwatch and a countdown timer.  No heartrate.  But honestly, anything beyond keeping up with intervals is more of a distraction than a training aid.

B5MN7, I have a Garmin 735 and it is great (thin, light, the battery that lasts 2 weeks, and it has all three sports).  
If you are already using an Apple Watch, it might be tough to let go of the integration to your (presumably) other apple products. The great thing about the Apple Watch is that you can not only have workout tracking but also guided workouts through the Swim.com app. USMS has a partnership with Swim.com and it integrates with the Workout Library. 
I have never tried Coros so can't speak to that. 

Thank you so much for all that great information! this helps so much!

Thank you so much! I'm not sure if it's just because my Apple Watch is older, but the swim.com app never really worked. It would glitch out so much, I was having so much trouble. maybe that's just how the app works? 

I have the latest Apple Watch. Loved my previous one but the new version pauses my workout for no reason. Almost as if the current causes it. 

I (re)started swimming 4 months back with Fitbit Charge 4, and then switched to the apple watch ultra. Having used fitbit/Samsung and apple ultra, I feel ultra is the best watch there is for swimmers. 

Stats are rich and detailed with heartbeat, auto-detected swim type, this watch is actually designed for Divers, with 3 days of battery-run and better integration with iPhone makes it stand out. 

https://www.apple.com/apple-watch-ultra/ 

I used to use an Apple watch until I got Ciye goggles. Now I  use both. The watch is still great to get my heart rate and cumulative number of laps—but nothing beats the goggles for splits. I did the one hour swim using the goggles and I knew with every turn my pace which was so helpful in keeping me on target.