Definitely a male, females lay eggs regardless if a male is present or not. For your first time, a male will be better as you won't have to constantly worry about eggs and something going wrong. Get some experience under your belt before buying a female.
10000000% male unless you get a live bearing species like a femal jacksons. Most female chams will lay infertile eggs like a chicken (without a male). this puts stress on the chameleon and will only cause problems with eating and drinking if your not looking to actually breed. Just my 2 cents.