Recent Chessmaster versions have many options to set for longer games, where it will use its time for better moves, except when its using its opening book and endgame database. Fritz is stronger, Chessmaster has the nicer interface, I've used both in the past. Fine software, though I'd pick CM for kids.

Unless I'm very much mistaken, little changes have been made to CM since CM9000, which is bound to be cheap. Don't know about Fritz's changes, but I think its changes were more extensive since Fritz8. Crafty is nice and free, but doesn't come with the interface niceties.