A few observations:
We have a diverse set of city, county, university and state park trails. Some are rail trails while others aren’t. The real rail line conversions are very smooth and flat and pretty easy to manage.
In winter, our crushed stone trails are always saturated, so they are either frozen or muddy. Small knob tires that clear mud well are ideal for that.
I find that riding 2” wide tires means things always work out. In particular, 26x2.2 Race King Protection tires are almost unspeakably good for our trails. The bigger sizes (27.5 and 29) are equally great. I keep one on the front mostly and run one in back in winter.
I use clip on fenders (SKS Beavertail) when it’s really muddy in winter, which means there is much less of me and the bike needing to be washed off in near freezing temperatures. No stays means no issues with the little sticks and debris that get kicked up.
People ride these trails on skinnier tires. I ride my other bike with 700x32 smooth tires on most of these trails in the summer when things are dry and not flood-damaged like now.
I really enjoy riding the trails. Definitely more than roads these days. I only ride roads to get to or connect to trails. Have fun!
Otto