You want your more aggressive tire in the front because when you're going around a turn at speed you Don't want your front tire to slide out. Under-steer is a bad thing when you're on two wheels. The tire with less rolling resistance would also be good to have in the rear because that's where your weight is most of the time. Less resistance where the weight is equals an easier and faster ride, and the weight also provides traction there anyway.

I have no idea how skilled you are, so disregard this if it doesn't apply, but I'm finding the more I ride the more I learn to find traction just by shifting my weight, getting lower on the bike, evening out my pedal force, etc. I'm still pretty new to mountain biking in particular so I'm still learning better technique with such things.

EDIT: Or see the post victim made while I was typing for the nice summed up version. Either one will get you to your answer.