Virgin,
Go for the palm. It`s the only one that actually does fit in your pocket.
If you buy the new m505 model, you get a color screen (not available on psion), a memory expansion slot, word and excel compatable programs that let you edit and sync with your pc. And if you really want a keyboard, buy the GoType keyboard for $89,-, it`s a real-size keyboard, except you don`t have to carry it around all the time as with psion.
A last thing: there are literally thousands of palm programs available, against maybe a hundred psion programs. Palm is the standard.