I've been reading and enjoying Irredeemable from the beginning (although I am considering the leap to trade). I meant to buy Incorruptible, but missed it somehow. Now that it's several issues in, I'll traidwait and see what happens. So i guess the answer for me is Irredeemable by default.
The only thing about them is that they're written by Mark Waid - so he'll be off them any time now.
Irredeemable does have this odd feeling that the story is already over but no one told the writer.