I'll go with Might and Magic III. Mainly because I haven't got a chance to play it yet. From what I hear, it takes so damn long to actually finish it that I would probably be able to replace my entire collection before I actually beat it.
I have that for the PC, and its so f***ing long you can play for 15 hours and have to start over.
Heroes of Might And Magic is as addictive as Warcrack, I warn you.
I love might and magic III but it is not my favorite game on the PCE since I prefer the Xeen saga of M&M more...
if I was being robbed of my collection and could only save one game I would save Exile II! because the rest of the games I have will be easy to find after I get my insurance check to replace everything.
especially cosmic fantasy 2. Theres only 39884093834 copies for 5$ new on ebay,