I can speak on this because I have trained with every tool we are speaking of.
Batons: I have hit people and been hit with batons during Non-Lethal Weapons course. Batons are not an effective weapon overall. Sure, they can break a bone but that's not what you want when using it. You want to take the person down. You want minimal damage when using weapons such as these. If I'm using a baton, I'm obviously using it because I don't want to kill the person I'm using it against. Well, if I don't want to kill them, why not make the pain as humane as possible? Ending up with a broken bone is not my idea of humane.
Pepper Spray: I have been sprayed with military grade oleoresin capsicum or OC spray. Commonly called pepper spray although the military grade is much stouter than what you can get on the civilian market. Anyway, pepper spray is not going to kill anyone, unless in a rare case of allergies or something. It can blind you if used improperly however. No amount of training with this stuff can factor out the human factor. In other words, you never know when the guy you are trying to spray will get a wild hare and jump at you while you are deploying your OC spray. If he's too close, it may hit him in an exposed eyeball and possibly blind him. Also, OC spray sticks with a person for a LONG time. You can be in almost unimaginable pain for hours after it being used. I don't want to deal with someone in that kind of pain if I'm a cop. Why? You never know what they're going to do. Finally, some people are immune to it. A smal portion of the population, but some are.
Taser: I have been tased. It sucks. It made me piss myself. You know what else it did? Incapacitated me. I was at the mercy of whomever was in the room for that brief time. That's what you want if you are the cop. The person endures pain for the shortest amount of time why also being made completely docile so you can cuff them. Studies have shown that 99.7% of individuals that have tasers used on them do not die. In a perfect world, that number would be 100%. But, this isn't a perfect world. I would offer that the small percentage of people that die from tasers is far outweighed by how many have died from physical altercations with cops after they refuse to comply.