I believe it really depends on your geographical area.  Like, in Chicago, many of the ladies will have on their websites that RoomService2000 screened is okay.

Personally..

I do not have a preference I am a member of both sites.Many ladies are members of both sites or just one it depends on what city you are located in and which site is used more in that city.They are very similar.

In my experience there doesn't seem to be a preference among providers.  Having just one would be fine, but with two I feel I'll have fewer problems.  Works fine so far.