I've got 2 bogens:
12ft generic
7ft fob
My 12ft gets reserved for major clamp parties or when I know I'll be at a bar that I can spread out the footprint and get away with extra height. It's primary use though is outdoor festivals where I can fly open.
My 7ft is the go-to stand, and it has a tiny footprint. I also use it for onstage taping as the smallest it will go is 18 inches off the floor, so I can run it without impeding others.
If you only have cash for one, I recommend the smaller 7ft as a starter. Most occasions when you can run the much taller stand, chances are someone else will bring one and you can just clamp on. In that light, getting a superclamp and an extension arm would be my second choice over the 12ft as well (unless you do plan on running a lot of stuff where you can fly high and there probably won't be other people).