I am Taser and OC pepper spray certified and I teach citizens how to use both.
Taser Brand devices made by Scottsdale AZ based Taser international are going to deliver patented neuromuscular incapacitation. You won't get this with a stun gun or any other electronic control device. The effect (when used properly|) is overwhelmingly effective. You can see and hear what's going on but you can't do anything. You can't control your movements and you lock up ridged as a board and fall down. The Taser C2 will go for 30 seconds allowing the user to drop the Taser and flee the scene. Call Taser and send them your police report showing you used your C2 Taser and they will send you a brand new one.
Pros:
It is the only device short of lethal means that can truly immobilize an attacker.
It only affects the person hit with the probes.
The laser sight on the device alone is enough to de-escalate less lethal encounters about 80% of the time.
CONS:
Both probes must hit the attacker to work
Standing too close you won't get a good probe spread and it won't stop the attack
You only get one shot
If the attacker is wearing thick or baggy clothing it won't work.
It can be used as back up drive stun device but it is pain compliance only.
Tasers have a 5 year expected useful life and they do have issues from time to time. It is an electronic device and can't be dropped and you can't get it wet.
Pepper Spray: Causes involuntary physiological effects on most subjects.
Pepper Spray is an inflammatory agent and it causes dilation of the Capillaries in the eyes causing the eyes to forcefully shut. Breathing int the agent causes inflammation of the respiratory tract reducing breathing to short shallow breaths. Skin contact causes intense burning sensations.
Pros:
Can be used on multiple attackers if needed.
Inexpensive and has a long 4-5 year shelf life depending on brand.
Causes involuntary effects and is very distracting. In most attacks the victim is able to shoot the stream in the eyes causing the attackers eyes to shut. This gives the victim time to get away.
Can be exposed to water and dropped without damaging the device.
Cons:
Is effective only when it hits the face.
If using a fog or cone spray it can blow back into the users face. Stream is best for outdoor defense. Use cone or fog sprays for indoor defense to run someone out of your home.
IF used indoors it can evacuate a building. This happened when one of our students had a friend set her Spitfire Pepper Spray off after thinking it was a flashlight.
So to sum this up both can be useful and both have advantages and disadvantages. I recommend Pepper Spray over a Taser as in field use they have about the same effectiveness rating (when you account for missed shots or thick clothing with Taser). The Pepper Spray gives you the advantage of multiple shots and regardless of what you have heard the right brand of OC Spray is debilitating on most people. It is a distraction device and it certainly will distract.
I have heard some good things about the Pepper Blaster and some bad things such as missed shots. Here is an article where someone used it and missed with both shots.
http://gunnuts.net/2011/10/21/effective-pepper-spray/
I prefer and recommend Sabre Advanced 3 in 1 formulation to my students. Sabre combines Red Pepper Spray with CS Military Tear Gas and UV Dye. This formula combines the inflammatory effects of OC with the severe facial burning of CS Tear Gas. Sabre Red is also a good choice.
Hope this helps and stay safe
P.S. Most people are instantly thrilled when they find out their pepper spray shoots 25 feet away. However they won't be using it that far away. In over 90% of confrontations Pepper Spray is used at distances of 4-6 feet. Also, many people don't understand that in a court you will have a hard time justifying someone was a threat to you if you sprayed the person across the street. A good OC spray only needs to spray 4-6 feet to be effective. The Sabre units fire 10 feet but they do make some that fire 18-25 feet away.