If you are concerned that your head might be a bit funny shaped then I say go with the longer hair. It's true that longer hair often looks bad on black men but it's because they tend not to do anything with it beside run a comb through it. There is a lot you can do with longer hair though...perhaps put a nice curl in it: link or have it texturized: link
If you don't want to put any chemicals in your hair, my guy friend gels up his long hair and kind of like twist it around his finger to make sort of a curly look. I'd show you a picture but I don't know if he'd want his big black head on GAG lol.
And just my personal opinion, but I think twist look better on black men that cornrows. Cornrows I think are great in the summer but when you out in the professional world or just even going to school they can give off the wrong impression. I think twist can be done in a really classy way though: link