guys,
it's like asking the best linux distribution or which of vi or emacs is the better.
hint - there is none, only personal preferences. some tools are best suited for some jobs.
In the ER, I could not have had a clamshell - it wouldn't have survived. The 6000 was the tool, with everything I needed. Now I have a 'desktop' life, a clamshell could be nice, to sit on the desktop, and to read email. If I have a 'field' life again, I'll need a portrait mode pda again, to read ebooks.
Therefore I am considering a clamshell Zaurus (that or a small base which could hold my 6000 :-)
My conclusion so far - even if the form would best fit my new needs, they miss far too many features currently. wifi is the bare minimum IMHO.
I won't take one until it has at least bt,wifi and gsm - which I could try to hack too :-) In the worst case, I can put a microdrive in my 6000 if I want, and I have an external BT keyboard much better than the tiny keyboard.