I think CC has been tinkered the most, with Card Sharks being a close second.
CS had the MC rules modified several times during the 78-81 run. At first, you could only change your first card at the bottom level, later all 3 levels' base card can be turned, then (along with the excessive $500 bonuses) the push rule (which was carried to the Eubankseses' version).
If we fast forward to the Eubankseses' version, they still had the push rule. The cards could now be changed anywhere, at anytime (which is a good thing since if you had an 8, you can change it more than once). They later tinked that so it'd be one card per line. That was just as good too (compared to the Perry MC).
The MC was also modified because of the car game, which is good and bad. Good because its a $10K+ car, bad, because it already slows down the progress of the show.
Lets not get started with the Bullard Version, albeit a $51,800 jackpot possible ($27450 was the highest ever won on this version...why I know this? I had the gall to actually tape the episode)