I own both the 9th and 10th editions of CM.
I prefer the 10th edition for the tutorials. The playing engine itself is a bit strange imho. The personalities will play unevenly. For stretches it will play flawlessly, then play nonsensical moves. I guess this is the way it brings the playing level of the main engine down to us mortals.
I decided to purchase ChessMaster. Does anyone have an opinion regarding which version is the best? I'm around the 1700 level.