I am moving from a Note 3 to an HTC One M8 tomorrow, on the Android platform there is no spell check in native apps (I turn off predictive text), does Windows Phone 8.1 have native spell check? I haven't used a Windows Phone before.
WP8.1 has a great keyboard. I use Android as well and I can tell you it's far superior. I'd recommend keeping predictive text on with WP8.1. Also the swipe keyboard is fantastic. It's great for someone like me with somewhat large fingers.
Since you cannot change the keyboard in WP8.1 all the apps use the same keyboard and yes it has spell check built in.