It depends on where you are hobbying. ECCIE and P411 in Texas, for sure, but I travel to Minnesota a lot. Very little ECCIE presence. It is all TER and P411 in MPLS.
When I first started advertising it was on SFredbook but that site is not very big at all for Vegas and most of the ads are agencies now.I use TER and P411 the most but I also like Eccie.
I have to agree with Ava I have more cancellations from gents who found me here then any other site.I find Cityvibe works and Eros both work for me.
Date-Check I use as well there are other sites but these are the main sites that work the best for me where I am located.Really depends on your area because certain sites are used more than others depending on what city you are in.