I am a longtime Window Mobile user and have had the Advantage for over a year and half (that's a long time for me - but there isn't anything available in the US that beats it yet, so I wait!)
I use the phone without the keyboard attached most of the time and I have tried lost of different on-screen keyboards.
ShapeWriter is new (still in beta, but you can register and get it) and I love it. In fact, it is the only reason I am running the Advantage in its native resolution (usually I use RealVGA to run in 96 dpi.) Check it out.
(I am in now way affiliated with either software maker, I just like their products!)