I use GBoard but since you asked for favorite, mine is Word Flow, Windows Phone’s keyboard. When MS killed Windows Phone they kind of ported it to iOS but never to Android.
The Windows 10 keyboard is very similar to this Word Flow and the closest I’ve been to recreate it on Android is using RBoard and the Xbox theme but since I don’t have a real reason to root I haven’t done it again, so I’m just using the regular GBoard. Also, last time I checked (few years ago) the Xbox theme didn’t have a dark mode so that’s another reason not to use it.
I’d use SwiftKey but they keys are to thin. I’ve tried using skins like the Surface Duo but still too thin for me.
Another keyboard I liked was TouchPal but I believe was removed from the Play Store for having malware, if I recall correctly.