I'm strong willed and so is dd1 and I started out spanking her when she was 18 months. I got a very angry baby and turned into a very mean mommy. It was not pretty.
We had quite a few scenarios of her doing something (say pushing buttons on the tv for example) and she would do it, I would spank, she would turn around and do it again, I would spank, over and over and over. Every time I got more angry and would hit harder and she would get more hurt, cry more and be more determined than ever. The only way for me to "win" was going to be to be a bigger bully and break her down. When I realized that, I started looking for other options.
She's still strong willed, but now it is something I love to see in her. I foster it and encourage it and it will serve her well as she gets older. She is also sweet, cooperative and helpful, because now we have a good relationship. We are on the same side, not adversaries, so her strong willed nature is not something I need to fight against.