I agree with most posts in here, but there actually is a distinction between a hot girl's and ugly girl's mouth. Getting a hot girl to suck your dick is far more of an accomplishment, and therefore more desirable. Getting dome from an ugly girl can be fine while you're in it, but after the thought that you just did that with a disgusting creature eats you away on the inside, and you don't feel right until you compensate for that with a hotter girl. But in the end, practically speaking, a mouth is a mouth, and slightly less attractive girls do try harder. But that feeling of disgust can be rough if you dip your standards a little too low.