Every tool has it's advantages/disadvantages
Pepper Spray
+ cheap
+ compact
+ easy to use
+ multiple shots
+ debilitating effects last 3 to 5 minutes
+ can be used in many situations
- some people are immune or can fight through it
- blowback in wind or confined spaces
Taser
+ Very effective, immobilization
+ Can be used in confined spaces or windy conditions
+ can be used in many situations
- expensive
- limited range
- one shot
- immobilization lasts only 30 seconds, no long lasting effects
- probes can miss or be blocked
Baton
+ Can be used for different situations
+ Range of effects from blocking to plain compliance to lethal force
+ Relatively cheap
- Must be close to attacker
- Can be taken and used against you
- Requires some strength and agility
- Requires training to be used effectively
- Heavy
Handgun
+ Used at different ranges
+ multiple shots
+ very effective
+ effective in most situations and conditions
- Expensive
- Legal ramifications
- Only useful for deadly force
- Requires training to be used effectively
The biggest problem with a baton as far as I can see is that it is seen as a less-than-lethal defensive weapon until you strike someone above the neck -- then it becomes a lethal weapon. Given that, the range of effectiveness diminishes greatly below the neck, so you have this tiny margin of effectiveness that may be illegal to use in most circumstances.
At least with a taser or firearm, the effectiveness isn't a major question mark, and the legality is well defined in most situations.
It reminds me of the advice, "Never draw your weapon to wound or fire a warning shot. If you draw it because you're in fear for your life, then shoot. Otherwise, don't draw."
For the baton, you can easily have the intention of merely defending yourself from a non-lethal fight (no other weapons involved), but then unintentionally inflict critical injuries as the fight escalates. Sort of the opposite of the above advice for guns: bring out the baton to avoid an ass-whooping, but don't use it in a way that makes it lethal.
I've even read using a baton on the knees also constitutes lethal force, but there was no explanation. Maybe because the baton can inflict irreversible damage to the knee? Just guessing.