YSK: If you make popcorn in a pot on the stove, the oil to use is ghee.
Why YSK: Popcorn fans often want a buttery flavor, but plain butter is a bad choice for popping popcorn in a pot, because the proteins and sugars smoke and burn around the same temperature where it's hot enough to pop the kernels.
Ghee, or Indian-style clarified butter, is butter that's been simmered and the milk solids (proteins and sugars) skimmed off. This leaves a clear yellow oil that doesn't smoke when it's heated and doesn't go rancid quickly, but has a distinct toasty butter flavor.
Vegetable oil is either flavorless or faintly bitter, and some high-temperature vegetable oils tend to start polymerizing (i.e. becoming plastic) when heated in small amounts. This is also not good for popcorn.
Good-quality popcorn popped in ghee reliably produces lots of "butterfly" popcorn with few unpopped "duds" and no scorched kernels or batches ruined by smoke.