i think this is difficult for me to answer since i've cracked passes and/or received passes to check all of them out... and they all get kind of boring... one site isn't enough. and paying for many sites would get too expensive... so i don't know. the most popular sites are popular for a reason... i guess i like them all. however, hardcore mediocre porn is plentiful.. so some of the sites i like in particular are classy softcore ones with kickass photography like bluenudes.com.
btw, some good site rankings/reviews at
http://www.adultsitesurfer.com and
http://www.x3guide.com (this is where i browse new sites to crack passes for)