The MSI and Acer have large keys with the standard US layout unlike the Asus which has fairly smaller keys and typing can be troubling at first. Also the numbers on the Asus begin right from the start on the left side with the tilde key missing so hitting the correct numbers can be quite messy. The needed pressure applied is slightly harder on the Acer keyboard, which I personally like, and the clicking noise on the MSI is fairly higher than the Acer. The Acer has smaller arrow keys and with separate PgUp and PgDown keys next to them, which I find more usable. The arrow keys are bigger and thicker on the MSI, but the Page Up and Page Down keys can only be used with the Function Button and the Up and Down Arrow Keys. Also the Fn Button is placed on the left down corner on the MSI, and can often be confused with Ctrl.
The most important thing about the keyboard would certainly be the layout. Acer paid attention to this part so I will again proclaim Acer as the winner here.
1st: Acer Aspire One
2nd: MSI Wind U100
3rd: Asus Eee PC