The trouble is, the 901 isn't out yet. Neither is the MSI Wind or the Acer Aspire One. Neither is the Asus Eee 1000.
Off the cuff, the one I suspect is the best overall buy for me, once it is available, is probably the Asus Eee 901. The 1000 is already approaching laptop size, and for me, the entire point of buying a mini-laptop is to have something ultra small and light. If I want the ten-inch screen and the various bells and whistles, I have a perfectly lovely Asus laptop.
The MSI Wind also has a 10 inch screen. Oh, I understand there will be a model with a smaller screen, but not one released in the USA.