I picked the Aspire. I like it. But I have PSU problems (?) I think like all the others who wrote reviews.
I looked into two others.
Shuttle - These are the 'smallest' but they have built in, proprietary, non-interchangable motherboards. When you pick the case, your picking the mobo as well. So I didn't like it at all.
Antec - Makes a cube case. But everyone I read has cooling problems with it, and has to add fans that only fit on the outside of the case.