I used Swiftkey for a few years while on my GS3. After getting the Note 4, I now use the stock keyboard and love it. I think the larger screen just does the trick to make the Sammy keyboard feel right.
Swiftkey. Using it since 2012. Allows and is able to actually use 3 languages at any one time. Working in a technically specific field it is important to retain my Dictionary
SwiftKey all the way. Tried the stock keyboard for about a week when I first received the Note 4, but switched it because I was so used to using it on my SGIII.