They can all be effective, Step, depending on the circumstances. Ever notice how many cops carry a TASER, and pepper spray, and a baton? It's because there's a time and a place for each. However, the armed citizen can't usually carry that much gear.
Pepper spray is the most affordable intermediate force option for the private citizen; call your local police department or sheriff's office to see what your jurisdiction's laws are on it, and also ask who locally can give you the training it requires. (The crime prevention unit or the department's defensive tactics instructor should be able to answer that for you.) The training is essential, but doesn't take long and doesn't cost much.
Explore likewise some training in the Kubotan, a short stick/keychain that's handy to have with you all the time. You can learn a lot to do with it in a four-hour course. The same techniques will work with a Mini-Mag flashlight which is legal to carry even in courthouses and aboard commercial aircraft, and is always handy to have on your person in any case.
Canes and walking sticks can be tremendously effective, but training takes somewhat longer and is harder to find.
Finally, don't neglect hand to hand training, if only because sometimes bare hands are all you'll have. If you're not in the best physical shape, look for entry-level training in Aikido or Judo. Judo programs are often very affordably available through the local YMCA. These arts are "low impact" and can be tailored by the sensei to those who have physical disabilities. A bonus is that they both start early on with ukemi-waza, techniques for breaking a fall, which are useful for us geezers even if we never get into a fight.
best of luck,