Probably neither, at least right away.
Yesterday Apple finally unveiled their tablet computer, the iPad. Which means that after weeks of rampant speculation as to what it means for comics, there's finally something concrete that can be considered.
Apple has decided to use the open ebook standard EPUB for their new iBookstore and reader on the iPad. Which is great for mostly textual books, but not so good for highly graphical publications such as comic books. This means that it is highly unlikely that publishers will offer comics and/or graphic novels directly through iBookstore. Thus, comic distribution on the iPad will no doubt be tied to a number of different 3rd-party apps, such as comiXology and the like. So instead of there being one place on your iPad where you go for all your comics and other reading material, you'll need to fire up a bunch of different apps, each of which has a different interface, different agreements with different publishers, and different pricing schemes. In other words, kind of a mess that won't make it easy for the casual comics reader to decided to download the latest 'it' comic that they hear about on NPR or see a review of the the New York Times.
I could be wrong. Jobs casually mentioned textbooks being part of iBookstore, and in the case of many math- and science-related textbooks there are graphical challenges as well, so maybe there's a plan to support formats other than EPUB in the iBookstore at some point. In which case, we'll be headed down a different rabbit hole all together.