A:
I would say buy BOTH! The minis are great for easy warmth, but they do let some air in around your ankles and when your feet are so cozy and warm it is quite shocking to feel that.
After first buying the minis, I tried my sisters short uggs on and fell in love instantly! They are even warmer and keep your ankles warm and cozy as well as your feet!
I would also suggest you buy small because these stretch out quite a bit once you break them in. I take an 8.5-9 usually and I bought my second pair of uggs in a 7 and they are perfect once you break them in! They are so much warmer when they are snug to your foot!
Enjoy!