Welcome to the forum.
First, you have to understand that Dell has two different models called "Mini 10". The older one is the "Inspiron 1010" and has the Atom Z5xx processor and GMA500 graphics. This model has a flush screen and HDMI video out. The memory is soldered onto the processor daughterboard and is effectively not upgradeable. The processor is slower than that of the others listed here. An integrated TV tuner is an option.
The newer Mini 10, the 1012, is based on the Atom N4xx processor and GMA3150 graphics. Memory is upgradeable (up to 2GB in a single DIMM) and the screen is not flush. This one has a white bottom shell and the screen is hinged forward of the back of the unit. It can fit a 6-cell battery without it sticking out. An integrated TV tuner is an option.
The 10v is based on the Atom N2xx processor and GMA950 graphics. Memory is upgradeable, though you have to disassemble the unit to do it. This is an older design but is the only one of the three that can run OS X, if you are of a mind to do that.
As for software, they're all equally capable.