I've played and finished multiple times:
VI, VII, VIII
I've played but not finished:
V and IX. IX was a complete disappointment.
Might and Magic VI was one of the first (serious) pc games I've ever played :)
I still think, Might and Magic series, one of the best rpg series of all time. I could still play them easily today. In fact the last time I've finished Might and Magic VI and VII was about 1,5 year ago, after I've found them again on GOG.
I wait for Might and Magic X to be released and I might as well get it on UPlay early access.