Sadly, there are no good dictation programs for the Mac OS.
I use both Dragon Dictate, and Mac's built-in dictation program. They both fall short.
The two main problems I encounter with Dragon Dictate, is that it simply will not work with Firefox. Also, it will often create random characters and move around the screen randomly. You can read about this on the Dragon Dictate user forums.
I find Apple's built-in dictation to be a bit better. Its main defect for me is capitalization. It simply does not recognize capitalization commands. I dictated this response completely using apples built-in dictation. I made no corrections.