I have a 904HA myself. I like that it came with the 6 cell battery and a 160GB, I believe most Aspire One models come with a 3 cell. You can buy a larger battery for them though.
I believe Aspire One models that compare to the 904HA are priced about the same, roughly 350.
There is one thing I dislike about the 904HA though, and that is the wider bezel around the display. The display itself it bright, crisp, and clear, there's just a wide bezel that seems to serve no purpose.
I was originally torn between the Aspire One, the MSI Wind, and one of the EEE models. They are all solid machines and most have similar spec's. Most have an Atom, 1GB of DDR2, etc, so they are all going to perform similarly. Best bet is to sample them yourself at a B&M store before you buy.