Swiftkey is hands down the best keyboard for Android I've tried and the only one I use now. The best keyboard layout I've ever used is called Fitaly (http://www.fitaly.com/) and it is lots quicker for single hand typing than anything else I've seen.
Due to licensing it would probably be hard to get this layout added to Swiftkey but I would love if it could. If the feature was there to pick my own letter placement on the keyboard layout, I could have the best of both worlds with the great prediction and the layout I wanted. Maybe in a slightly more expensive "Swiftkey Ultra" version? I would upgrade for that!