For long-term stability, I would say Debian is definitely the best choice. The current stable version is Squeeze but the next one, Wheezy, should be coming this summer.
Performance-wise, going with the armhf (hardware floating-point calculations) version of Debian that was released in February, along with the imx repository that was just posted a week or so ago (check the Debian section on this forum).
I'd say, when you install the armhf image, set your repositories to the Wheezy ones, since it's pretty close to being finished. I'm not sure if the Wheezy imx repos are ready yet, but I think they're coming. I guess technically since Wheezy hasn't officially been released yet, you might want to keep an eye on it at first but I think you can generally be pretty confident in it.
If you want to be super-confident, you'll go with Squeeze....but I don't know what the status of the armhf builds for that release is.
Squeeze is armel only. that said if you just want to use it as a server, my headless image should just work. I also have a headless image for wheezy as well. which is armhf.
I have compiled the genesi specific packages for squeeze and they work rather well (better than maverick in fact) I will see if I can get them put into the repo. but I doubt there will be any updates to them. Is anyone using squeeze on the efika as a desktop?
Senior Software Engineer
Genesi USA, Inc.