For me it's either one, so circumstantial. I wish you had added a third option.
I've done the base dungeons on normal and hm too many times to mention so yea I don't mind speed running those.
The harder dlc vet dungeons with randoms can be tricky cos some are high damage and some newer players don't know mechanics or underestimate the damage mobs and bosses do in there.
I do enjoy doing the secret bosses in the vet dlc dungeons. When everyone plays their role efficiently it's fun.