Probably the biggest thing to take into account with tires, is what were they designed for?
If you ride a lot of roots, and rocks, which may be wet, you will need a different tire than someone who rides pretty much only dusty trails.
Hard, dusty?
Bontrager: XR1 Team Issue (Model #11869)
Lots of rocks/roots, or softer dirt?
MICHELIN Wild Rock'R Advanced Tubeless - Tires vtt | MICHELIN Motorcycle - United States - Bike-website
Take into consideration, if you ride a lot of the above mentioned rocks and roots, which may be wet, you will want a tire with a softer rubber (durometer), and a lot of siping on the tread.
If you ride a lot of deeper, higher traction dirt, you will want a tire with larger knob depth.
If you care only about traction, don't worry too much about ramped knobs and avoid a central knob pattern.
Hans Dampf | Schwalbe North America
My current favorite -
Bontrager: XR4 Team Issue (Model #11643)
If you only care about speed, look for a tire with a nearly continuous central knob pattern, and ramped knobs. Example -
CrossMark | Maxxis USA
Then you have tires that have ramps, deep knobs with no continuous central tread, siping, and evertything. They may not excel at anything, but they may do everything well. Might be a harder tire to pedal. Example -
https://www.kendatire.com/en/bicycle/mtb-trailall-mountain/nevegal-x-pro/
So on, and so forth....
My 26", I currently have a
Bontrager XR4 in the front, and a
Specialized The Captain in the rear. I can so far find no faults with the XR4 at all. I love that tire. The Captain, when it is dry, excellent. Wet, I spin on rocks and roots. The central knob pattern just does not get as solid of a grip on the wet stuff.
My new bike has
Bontrager XR3 tires. I cannot complain about them, but I have not had good riding weather (snow) to compare them too well. My brother has
Maxxis Minion tires, and he said he was dissapointed in the traction of those compared to the XR3s in the wet/snowyish conditions we have had recently.