Wii Sports is a great multi player game to include with the Wii console.
Baseball: Probably the worst of the 5, baseball really only allows you to hit and pitch.
Bowling: Probably the best for multiplayer, bowling is best adapted for the Wii remote. It's really fun to compete for the best score.
Tennis: Wii Tennis is amzing. Swing the racket to hit the ball. It's really that simple.
Boxing: A little too complex, and a little bit difficult at times. Golf: Golf is HARD. This game really depends on your luck and how hard you swing the Wii remote.
P.S. - My favorite out of the 5 is probably tennis or bowling.