Hi,
R12 it's the best for me, 5[K] of very good printed documentation (hard cover version of the user manual), stable, DOS+Windows, DCL, fast, render, SQL connection (ASI remember?), great fun with ADS (I know ADS is a little older but this version was a lot better), great ADS examples from JW in person. Still have a CD (from Autodesk) with a lot of resources for programmers.
Gaston Nunez