We've asked it a few times before, but it seems like every season there's another tire size that's supposed to be the next big thing. Last year we saw the bigger 2.8"-3.0" plus-size tires fade away in favor of 2.6" options, while there's still a strong following of 2.4"-2.5" tires.
The XC crowd has foregone 2.2" for 2.35" in many cases, and even wider at times, and trail riders are constantly debating as to whether they want more traction or less rolling resistance. The amount of riders realizing you can pedal uphill with ease and still get down quickly on an appropriately spec'd bike has grown to the point that downcountry actually is a thing, and bikes can transfer from pedaling trail in the morning to doing laps in the bike park in the afternoon by simply throwing on a full face helmet.
No matter what you ride, tires are one of the most important elements of the experience and the width of your tires directly impacts a lot of the handling and feel of your bike.
How wide are your tires? Answer both!