Portrait - Swype
Landscape - SwiftKey (Smart Keyboard a close second).
In portrait mode, I prefer Swype. Some of the qwerty keyboards are a little to small for my fingers in portrait mode, but my fingers can fly using Swype.
In landscape mode, my fingers don't seem to flow as well with Swype. I guess it is finger-memory on the smaller (portrait) Swype keyboard. I do a lot better just typing things out with my thumbs. I keep going back and forth between SwiftKey and Smart Keyboard. With SwiftKey, I keep watching the word bar and can move pretty quickly. With Smart Keyboard, I tend to watch my fingers more, so that slows me down a tiny bit, but autotext does help to speed up typing.
I haven't rooted yet, but once I do, I'll add in Keyboard Manager so I can have keyboards switch depending on orientation.