Starting out, I switched between the Samsung and Android keyboards. Both were pretty fast, but I loved the XT9 system on Samsung. For a while, I tried Swype, but I just couldn't do it. It wasn't meant for me, though I believe the concept is pretty good. I tried the Droid X port and it was nice, but I still didn't feel comfortable typing on it. I currently have the HTC IME and the Swiftkey keyboards on hand. My preference order is:
Swiftkey
HTC IME
Samsung Keyboard
Samsung would be a tie with HTC IME because of multitouch, but it lags and I have an issue with how it deals with punctuations on its layout.