Actually, my chosen format is eReader (formerly Palm Digital Media ereader).
Yeah, it's got a DRM format but it's also got a DRM-free format, and you can make your own books. It runs on Win, the Mac, iPhone, WinMob, some Symbian, Palm, and some others.
I've used Adobe's protected format and it's an invention of the devil him(her?)self.
I hate it so much that I've actually gone and repurchased anything in Adobe format in eReader format.