Distance is key in my opinion - a knife requires close proximity which, if the opponent is smart, can end up not so safe. You can end up with major head and vital organ damage with the bat. Plus, you have to be quick because you won't be able to stay in close for very long and have to be VERY accurate hitting something that will stop your opponent.
A bat can be used to crush, jab, and push. Disarm your opponent by breaking an arm or hand, or shoulder, or anything, and you see yourself with both a bat AND a knife!
I choose bat.
Never argue with an idiot; they'll drag you down to their level and beat you with experience." ~ Anonymous