A bat or knife could easily be taken away by someone with a little training and then used against you.
A good point. A swung bat is very easy to take away from somebody. I've seen it happen. I would opt for something I could jab with. Force is concentrated on a smaller area and you retain better control of your weapon. I think a 1" or 1 1/2" dowel or a closet rod would be a better option. You can also jab a lot faster then you can swing. Throw a dozen fast jabs to a person's face and belly. Check out the US Army combatives manual on the
three foot stick