Ask YC: Should I use a framework or just write the code myself?

I'm about to start working on a new web application and have been looking into different frameworks (such as RoR, Django, symfony) to see if it makes sense for me to use one. I have to say that every time I read about one I feel like I'd be constrained by the framework for not a lot of gain.

Do YCers here have experience with or without a framework? What would you choose?