This would be my choice. I played it a lot when I was young, building huge bases in the levels that supported them and unleashing armies of Rock Raiders and vehicles on the environment. I'd like to be able to jump on and play it for kicks every once in a while, but no computer I own now would run it. That said, Rock Raiders is long gone, so this would likely never happen.
I would like to see MNOG revisited: basically as it was, but with more consistent and detailed art throughout. Also built with something other than Flash, since it's quickly losing support.