The guy asked for "active."
Bigfoot is in Europe, and if you are an US player there is no sense in going there and struggle with a 130 ping. Plus the most players I have seen there are 3 and in the morning - U.S. time. I personally can not play with that ping and I would only go there as a last resort. Not fun at all, at least not for me.
Fear is empty all the time if not most of the time.
Co-op is always empty unless you invite someone.
Therefore, *shrugz* it seems as if Shmack is indeed the only viable option to find a populated rune Quake game as the original poster requested.
A quick glance at the server browsers, here
http://www.runequake.com/servers/ and here
http://www.quakeone.com -> the splash page, will tell you, in fact, that I am correct.