If I can race anywhere, I choose STCC servers. They are very well regulated and I almost always find a clean race. I think they should expand the current STCC, but as the community has said, some people just don't want a system that filters out the n00b crashers. People might just want to race any car they feel like without demonstrating that they can, therefore not wanting a licensing system.
To each his own, I think the way it is now, having both options is great, but as I said I would like to see the STCC expand in some areas.