My girlfriend exercises her pussy muscles, and I love the way she grips me when I'm sliding into her. She also has this sort of ripple technique where I feel her working up and down my cock. An ass feels different, whether it's my girlfriend's or my fuck buddy's. It's partly the resistance when you start sliding your cock in, partly the way the lube you use is at play, partly the incredible feeling of ending up balls deep. But comparisons are tricky. Every pussy is different. Every ass is different. I know I'm lucky with the people I'm currently fucking.