Because of the whole interface and the many options I have to talk about music with many different people from many different countries, atrl is definitely my favorite forum. In general, I would say I like forums involving statistics, especially soccer statistics. Ironically, I'm very lazy at checking at current music charts, such as iTunes and Billboard. I guess I'm better at creating my own music charts with my own musical taste, a.k.a. My weekly music countdown, haha.
These last weeks I have seen many threads created for languages besides English, therefore many of them working as grammar checkers. If you are learning a second, or maybe a third language, I would recommend you visit wordreference.com. I find it very useful and it helped me with a lot of doubts regarding English grammar/lexis.
I lol'd irl. 