Primarily slow spin in the 80 rpm range but will frequently stand for about 20-40 pedals to work different muscles and give my behind a break.
Much depends on the steepness of the grade and length.
If in the 10%+ range, I will mostly sit and spin out of fear of blowing up before peaking.
My road bikes are 34:34 and 30;27 low gear ranges and my rigid MTB that I ride on road is a 24:34 so I have very low gearing to spin.