Boots for most, but only because of the mud, puddles and rain and I use lowa renegades which are quite light anyway. I've been up mountains with them no probs and did the salkantay trek to machu pichu with them. Boot nazis will tell you the renegades aren't suitable for mountains so apparently I've defied physics
Comfort wise, trainers all the way. Trainers only really get used in summer tbh.
I've just got some altra. Haven't used them yet, but they're all using them in the states for their long distance trails.
The only other thing is if you're going on a really rocky mountain your feet can take a beating so again tougher soles can help there.