I would try to aim for more of a balance of both. Maybe make the lower levels more of a group combat challenge with a few puzzles you don't mind if they get leaked, aka root quest, or something like that. Then maybe the upper levels or secret chambers that would contain the puzzle like things that one player could get into without having to go through the group area. Maybe make the secret chambers/levels of the tower more of an imm reward, or at least easy to ban players who abuse it's knowledge. This way you can hopefully make more people happy, the people who want to challenge Hell but can't (AKA Goodies) and the explorer types who like puzzles, and yourself because you'd only have to change a few puzzles or ban a few people if someone posted.

That which does not kill us,
makes us stronger.