I've read that for the same tyre construction and pressure, wider tyres will roll easier because they have a shorter (lengthwise) contact patch with the ground (ie for the same pressure, the contact area remains the same, but on a narrower tyre this area must be longer and narrower and consequently deform the tyre more), and will also be more comfortable. This seems to make sense to me.

I'm running Maxxis M-Tread's, 2.10 in front and 1.85 in rear. They seem to roll pretty nice. I'm finding much more enjoyable to ride on than the narrow tyres I was riding previously (though it's also a different bike, so ymmv).