You're talking to the right guy. I have had hip problems for a couple years, so I used a cane daily for the last several months. I had my hip replaced in February and I'm weaning off of the cane while inside but still use one outside.
First, get one that is heavy duty enough for you. I got an adjustable metal one from the local pharmacy that supports up to 300 pounds, so if you are big make sure to get one that can support you. Some of them are only rated for little old ladies!
Second, my recommendation for a first cane is an adjustable metal one. They are cheap and you can adjust the height to find your exact comfortable height. They are light but still would be effective at warding off aggressive dogs because keeping your distance is most important.
Then go to a Tractor Supply, or similar store and get a heavy duty cane or "livestock sorter" as they sometimes call them. I got one that is heavy hardwood, I think hickory but could be different. You will have to cut it to length so be careful to make sure you know what length you want first. These canes aren't so much for walking so they didn't have a rubber tip to stop the end from sliding. I had to go to Wal Mart to get a tip for it because it was bigger than a standard cane. I found a tip that was supposed to be for a chair leg that was perfect. I thought I'd like the hickory one more as it is more "manly" but actually, it was kind of heavy and the crook wasn't as comfortable as the foam covered metal one.
There is a website for "fashionable canes" that has a wide selection. I didn't buy any from them because I found what I wanted locally. But that shows you a ton of options. They will also show you how to measure for the right length, if your local pharmacy or medical supply company doesn't adjust one for you. Canemasters also has a whole website dedicated to cane self defense.
Good luck.