I'm surprised only two other people voted for classic rock. Probably because it was paired with "pop rock", which is probably the shittiest type of rock in existence...
I can appreciate almost every genre listed there, and I listen to stuff in most of them on a regular basis...but overall classic rock dominates in terms of having a huge spectrum of really fucking good artists residing in the category.
Don't get me wrong, I love prog/psych rock, post rock, ambient, psytrance, etc, but the good artists are few and far between...lost in a sea of other artists who suck really bad.
Not to say there isn't shitty classic rock, of course, but the ratio of good music to bad music within the genre seems much greater than with any other.
Just my opinion, of course.