i have used a couple now, the first one i dont remember what company it was, i think hp and the 2nd was a samsung.
i just bought the samsung, first i went to a shop that i knew sold it and had a bit of a play with it. i was able to test it with everything i knew i would use it for. so i went on utube, bbc iplayer, facebook, quakelive, excel, ppt, word and i was comfortable with the screen size, 10". smaller is better for me because i will be able to carry it easily and the battery will last for longer.
One thing i found was that the shops have internet explorer with a lot of addons that fill the top of the screen, but google chrome is very small so thats what i use and i can see a lot of the screen. setting the task bar to hide when not using it helps too, but i find that quite annoying so i dont use that.
when i get a chance i will try and upload a screenshot, so u know what can be seen.