I've used a number of different handwarmer solutions over the years -- liquid fuel, solid fuel, and chemical.
The thing I like about the chemical packs is that they are very small and thin, weigh virtually nothing, and you can tuck them places where you can't put another kind of hand warmer.
The solid fuel ones are convenient, but they have a tendency to go out when you really need them.
The liquid fuel ones probably deliver the most heat, but they are also the largest. And fuel is geting to be quite expensive.
"The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza
Baby Jesus cries when the fat redneck doesn't have military-grade firepower.