I had apple watches and moved to Garmin 7x. It's extremely reliable and as good for tracking as apple watch. The error of margin is so small that negligible. If you want to be pro you need to go pro equippment anyway as both are not good enough.
Garmin is 20d+ battery and this is a killer feature for me. I hated and will hate apple watch for its battery, although it's a very good computer, though a silly idea to have a computer glued to yourself all the time, when I now think about it. All the smart features of apple watch were simply useless to me in the end