There are more Rugby fora than those mentioned in this comparison. The comment made is a good summary of the main fora using English language, there exist others in French, Italian or Spanish.
If I can make a comparison, the Kiwirugby and Silvern fern fora have more technical and strategical discussion than TRF. The people there have usualy quite a good knowledge of Rugby and its history. PR is very versatile, in the sense that it is a place where there are many discussions not related to Rugby. People there have usualy a good sense of humour and are rather tories when it comes to politics and this happens quite often.