What fluid for a 4-speed trans?

Generally speaking, if you live in a cold climate, use ATF, warm climate, use gear oil. I've always used ATF because I like the smooth shifting no matter what. I use it in Vixen's A903 three speed, which had a non synchronized first gear. Normally you have to come to a complete STOP before shifting to first, but since it shifts so smoothly, it goes right in from about 10MPH on down. Doesn't sound like much, but that's perfect for rolling stops.