First...
If you download a quest with a selfmade (multi-room) overlay, on which of those boards would it be easier to use the overlay?
I love to use overlays to change the room layout a little bit.
Second...
How important is setup-time and stow-away time for you?
I know for sure if I play with my 6 year old daughter, the setup is a crucial decision gate between "I want" and "No daddy I'd like something else".
If I play with my warhammer 40k club, setup is no problem at all as they are used to hours and hours of set up time
Third...
Pass through rock and dungeon exploring
The original heroquest board gives you some orientation, even if you never played the quest before. You can use "pass through rock" and walk into the dark, being sure you don't accidentally leave the board.
Also in normal gameplay, you can actively search for a way into the middle room. Search the forum for reports where the wizard passes through rock directly into ragnar's cell, for example.
The game play with a modular board is different. As a player, without the quest map, you never know which direction is the right one. That adds some sense of mazeness that is sometimes missing in the original.
The other extreme is a map of Heroicmaps, that gives away a little bit too much (except if you print it and set it up peace by peace).
Some people get so excited by modular boards that they never want to play non-modular again, other people hate it.
Find your own answers to these questions...

For me, the first question and my personal answer was the most important for me.