I avoid the Microsoft store on Windows but I use Steam all the time. I've also used Steam on MacOS for those few games that run on MacOS that I wanted to play.
I'd can see myself using other stores on iOS depending on the store. If Steam existed on iOS I'd certainly consider it, especially if buying a game that ran across platforms included the iOS version.
I use the MS store for MS software. But avoid Steam if I can as well as they also take a substantial cut (Although this does mean I still get a lot through steam).
Although they're more flexible, if a game sells you a CD-key outside the store (eg on Humble, through promotions, etc) they don't take a cut. Steam only gets it when it's through the Steam store.
