I use Smart Keyboard Pro. It has a small memory footprint, is simple yet has good prediction, and I found a keyboard skin that has bright green letters on black keys that matches the theme I have perfectly. I supposed it is not the most horsepower keyboard around but I like more of a modest utility, I guess.
BTW, if you do go with a custom keyboard you can disable the other two to save system memory after a restart.
I've about tries them all... Swype, Go, Thumb, stock, but I ALWAYS go back to SwiftKey. It is by far the best at predictions and I make fewer typos. My only wish is that they will come out with more themes. Totally worth the money.
I was using Swype but switched to Swiftkey 3 and will stick with this one. Definitely worth the $. As one poster mentioned, it is amazing at predictions. I type fast and not very accurately but Swiftkey manages to correct my mistakes with amazing accuracy. Hope this helps.
Swiftkey since beta and landed landed pro version free as part of Amazon's free app of the day. Swiftkey 3 is amazing at predictions, never looking back. It was so effective I ended up purchasing the tablet version for my Prime