I was using a Specialized Captain in the front and a Kenda Nevagal in the rear. It worked well for Mammoth last year, as well as Big Bear and all my local trails. Mammoth is loose and pumicey, Big Bear is a combo of perfect soil and loose & rutted out, and my local trails are a combo of things.

However, since I started riding more aggressively, I needed a fatter tire in the front. I now use an Intense 2.5 in the front (the fattest tire my rim can handle) and the Kenda Nevegal 2.1 in the rear. A fatter tire will give you more traction (great for berms!), but definitely slows you on the uphill and requires more effort.