From a behavioral perspective, I would say that it doesn't matter one little bit whether you get a male or female. However, I did vote female for a couple of reasons...
1) They tend to be more pricey... thus in my opinion better to get out of the way early.
and
2) If you plan to breed Corns one day, seems better to go ahead and start "growing" your female now. Your male doesn't have to be quite as old or large as your female to breed successfully, and you have to be sure that your female is large enough to handle passing the eggs.
If it were my decision, and I was only going to buy one snake now, I'd get the female. That way, in a couple of years when your ready to start breeding her, you'll be looking to purchase an adult male, which in my experience is much more cost efficient than buying an adult female.
Just my $0.02...