Me being a skinny guy with an open mind in experimenting:
Anal sex was easier with skinny girl. Easy to find the spot and angle.
Missionary and variants - skinny girl. Easier to hold her closer and tighter when going very fast.
Riding skinny girl. She could ride faster.
Doggystyle and variants - fatter girl. My bony hip was cushioned by her bum when thrusting.
Boobsex fatter girl. She could support my body weight.
Other than those, not much difference. I had a great chemistry with them - Both types are equally pleasurable in kissing, rimming, oral sex, other positions like lotus or sideways.
The fat girl I dated was 5'4" and 180 pounds atleast. Skinny girl 5'5" she was 120 pounds.