underdark or mountain pass?

just wondering which one you guys think is the most fun for a first time player of this type of game

ive already cleared the way to the mountain pass (pain in my ass) and ive solved the puzzle in the goblin area to go down the entrance to what i believe is the underdark

which one do you think is more fun? or more tedious? if one is easier should i just go for that to get to act 2 as fast as possible?

im level 4 and cant find anyway to reach level 5 at this point without venturing forward