I've use the Maxxis Rambler, Donnelly MSO and Continental Terra Speed. They all get fairly good rolling resistance scores and work very well. for general mixed surface riding. They have a little tread and a bit less in the middle, which will work in mixed surfaces, but won't work very well in actual muddy trails.

I always buy folding tires.

FWIW, the Terra Speed and Terra Trail are quite different, with the Trail having much more aggressive tread. The Speed is the one you'd choose for general, non MTB riding.

But I didn't see any major difference between the three I've used. I generally focus on 3 or 4 varieties and pick one based on availability and price.