I have owned the M1400 Tablet PC from Motion Computing for several years. It was the second generation device they produced. It has been a workhorse.
One of the key factors is looking at a mobile device is how many moving parts does it have (swivel screens are generally a bad idea) as well as how "sturdy" it is built to withstand shock, abuse and general daily rough treatment. I have put my tablet through the ringer and it still works great.
They now have a new model (same footprint 8.5 x 11 screen) and a 1/2 size footprint which is an ideal solution for the mobile professional.
I would recommend you do a price comparison against the competitive units (check out