I used to play at GameKnot. I was a premium subscriber there. However I quit because, firstly, my school and library computers use SmartFilter and I have to rely on Internet kiosks and friend's houses to play GK, thus suffering a lot of timeouts, and secondly, the forums were too liberal.
These aside, GK is a great chess site and you should seriously consider joining. My experience (even as a free player) there is way better of RHP (though RHP is also a great site) and after just a few months I was convinced to subscribe. The best rating I ever achieved there was 1650 though my average rating there is probably closer to 1400-1550.