I use the Michelin XC Dry2 and Panaracer Fire XC Pro tires; sometimes I mix and match them depending on conditions.

The Dry2s have much lower rolling resistance than the Fire XCs and work well on hard packed dry surfaces (duh right?). They tend to wash out easily when cornering in small gravel and sandy/dusty conditions and once the side knobs wear enough to loose their edges the cornering traction becomes severely compromised. Surface dependent, braking traction is good. I have had mine for about two seasons and they are in need of replacement. They are terrible for slime, mud, or wet rocks/roots; I made the mistake of using these at Blue Mound in slimy conditions. I have ridden these tires at Kettle in the dry and they worked well on the rocky sections and ok in the sandy bits. I use these tires most of the time.

I use Fire XCs exclusively when it is wet and/or extra traction is required (slimy hills, roots, wet rocks, snow) and they do the job. I used these tires at the 09 Sylvan swamp fest and I didn't have traction issues. Rolling resistance is high however and I can easily feel it when riding on hard packed surfaces. During hard cornering on hard surfaces there is noticeable "knob walk" with these tires. I have also lightly used these for about 2 seasons and the knobs are only slightly worn.

Looking at a tires tread pattern can give insight to how the tire will perform. Small short closely spaced central knobs are usually advantageous for dry conditions and low rolling resistance, large tall widely spaced knobs are good for shedding mud and digging in to the soil in loose conditions, and aggressive side knobs will give increased cornering traction in loose conditions.

With that said, tire choice is highly dependent on riding style and everyone is going to have different ideas on what is right for them.