I personally use SwiftKey. Been using that since the S2. It's aurocorrect is amazing and it's predictions work well. I paid for it (3 or 4 bucks I think) but the free version works fine. You can type really quick and it also includes a Swype option (they call it "flow") you can also let it scan your emails, Facebook posts, texts, etc and it'll learn how you actually type, memorize what slang you use, etc.
Lots of customization options down to the look, feel, what certain actions do (double tap space bar for period, auto caps, etc).
The straight up Google keyboard works very well too. There's also Fleksy which is still a tad new and a lot of people like it, just didn't work out that we'll for me.
Hope that gets you started!
Sent from my SAMSUNG-SM-G900A using xda app-developers app