Having used both, I'd pick the Acer. The 4G has a horribly small screen, cramped keyboard and only 4Gb of storage. FWIW; I'd try and find the XP version of the Aspire One; at $349 it has 120GB of storage, XP and 1GB of ram.

Also; the Eee 4G only has a CPU that runs at 600MHz, the Aspire one uses the Intel Atom at 1.6GHz, which is fast enough for almost anything you throw at it.