I'm seriously considering moving from a Garmin watch to the Apple watch but with Apple being more smartwatch oriented than fitness oriented, I'm at a loss as to which app is best.
Is there anything out there that would compare to the Garmin software or even the Fitbit app? I need to track daily activities (steps, stairs, etc.) along with tracking time on the treadmill and rowing.
Any suggestions?
None of that reads like you need the extreme batter life endurance athletes are after nor even a specialty app. Your first consideration should be that some apps use the phone and are not watch only. That can be a good thing where I'll use very big bike rides or skiing as examples.
I was a fan of the Abvio apps before I had the watches (Series 2 and 4 now). They're really the same app but default to the one you purchase. Mine's the Cyclemeter. It has mountain biking and skiing recording the stock watch app lacks but also imports exercise from the stock app and that's really nice if you want to leave your phone home. It keeps your data private or can export to Strava and other services.
Some friends use Strava that works without the phone.
You did post in Series 4 and I do suggest a Series 4 watch now that I've had the 2 and time with Series 4. The display is great and it has overall speed and performance including cellular that I appreciate. The Series 4 finger on crown to aid heart rate and facilitate the ECG help your sports apps get heartbeat in a hurry.
For battery management, basic good workouts have never caused a battery life problem with my 2 or 4 but rather "epic" days mountain biking or skiing have needed the way my Abvio app and watch can work together. These are when you have the GPS, HRM, speed & distance capture working for hours.
Finally, know the watch is really helping you have a baseline and know how to quantify what you do. As examples, my family members burn the calories at different rate than I do for same stuff, and a third party app can count them differently than what's built into the watch.
They're not for everyone but I see what many do for personal tech because I'm an IT manager by day and a leader in a sports club. Apple Watch has clearly had more keep using it than other purchases but people who do endurance competition still get some others for that special purpose.