I'm a believer in the theory that Delphi versions 2,4,6 were more bugging
and immature and 1,3,5,7 were the "really good" versions to use. D8 changed
that sequence somewhat due to the .NET fumbling but if you think of it as
just another even numbered version, D2005 is the one to use.

I would pick D7 or D2005 myself although D2005 has yet to have the desired
stability. Perhaps with yet another update to it.

I just finished moving all projects from D5 to D7 and am just waiting for
D2005 to settle down.

P.S. Always apply all updates to any version, of course. They always have
fixed real problems that you may very well run into someday.