Trousers off road riding = sweaty and most are flappy to catch on chainrings etc.
I find that 3/4 waterproof shorts and a set of winter tights with softshell shin area (Scott) are a great option. My calves/shin and feet get wet (bu then nothing keeps me dry here in winter), but do dry really quickly and are warm.
No place for long kecks on the mountain bike IMHO – v uncomfortable. Bib shorts / legwarmers with a waterproof short over top for when it’s filthy.
Bare legs with a waterproof short is OK as well, if it’s not very cold.
I wear my Gore Fusion MTB trousers loads beacause they are great. They are not particularly sweaty, work great with a softshell top/gilet and do not get caught in my chain. I also wear my Endura singletrack trousers alot because they are great aswell.