Most pocket/pc PDAs run TT. I had problems with the HP4700 and TT5 which crashed every 30 minutes or so, so I reverted to TT3 which is fine.
The Mitac 168, sold under various guises, is a really nice little PDA with a built-in GPS receiver. I have one of those - does exactly what it says on the box.
TT6 I can't speak for personally.