Hi misa, my preference is in this order:
Danger on Deception Island
Last train to Blue Moon Canyon
Curse of Blackmoor Manor
Danger by Design
Legend of the Crystal Skull
Secrets of the Old Clock
But not to upset the applecart! - Nancy Drew games vary & if you like tough puzzles you've been given very good advice by BrownEyedTigre & nickie - I have fond memories of Curse of Blackmoor Manor - it is the game that led to my 1st post on GameBoomers! To follow, Legend of the Crystal Skull might appeal as it almost entirely consists of solving a sequence of puzzles!