Tried SwiftKey on both iPhone and iPad.
No swiping for iPad, so uninstalled.
No access to voice dictation on iPhone, so uninstalled.
Both caused a slight lag bringing the keyboard up.
Auto correct on iPhone seemed like a pain in the ass, at least compared to the way the stock iOS 8 keyboard works- been on the GM since it was released so I'm used to that now.
Don't want to pay to try Swype- had it on Android years ago and it was cool, but I'm not gonna pay even one dollar to try it again if I can try out 'swiping' via the free SwiftKey. The only times I really typed one handed is driving... maybe it's not such a bad thing for that task to be a little bit of a pain in the ass so I'm not as tempted to do it.
Overall- I think I'll just stick with the stock iOS keyboard. It's done me well for a couple years and it's obviously made to work well with the iDevice.