What I use is WinRAR to access the contents of the ePub. It works very well. I don't need to rename the ePub from .epub to .zip ever. I just right click and slect open with WinRAR.
When I edited any of the files (non-graphics), I use Notepad++ as it works very well and has very nice regex. Plus, since ePub is split into multiple files, I can load all the HTML files in one go and do search/replace on all of them like they were one file. So I do not have to make the same corrections umpteen different times. And best of all, Notepad++ is free.