Hmmm, thats are hard one for me as I never really experienced a massive range of Amiga games as we couldnt afford many when I was younger.
For me I would have to say (in my opinion):
OCS/ECS - Simon the Sorcerer or The Settlers or Superfrog
AGA (native) - The Shadow of the Third Moon or Slamtilt
AGA (ported) - Simon the Sorcerer 2
