Male or Female.....which is better..first time breed owner.?

A man i know is getting a heeler this is his first heeler. He wants to do trials with it. In our trials here the dogs MUST be intact. Should i get him a male or female? He is having me pick out the puppy. Ive prefered males. The man said it doesnt matter as long as it will listen and be agood working pup. This is his first "hard" breed. He has had border collies before but NEVER cattle dog or anything with a dominate/willful personality.