ha ha i prefer manga as opposed to comic-comic books but in general, i prefer having the book in my hands! web series seem to be uploaded page-by-page and i don't have the patience to check back each time a new page is uploaded and i forget what's happened before so i gotta reread it. i guess i prefer volumes to single pages;;
Web comics. If it's primarily web comic, it can be both very very expensive to get the physical copy + less of the comic because it will be done on web first. (e.g. homestuck) Even ones which are primarily comic books still only take maybe a week or so before it's online. PLUS when you buy a comic book, you buy the book + delivery, and then have it take a while to deliver. You gotta do that for every single comic in a series. Online however, you can buy the comic, no delivery wait so it's right there as soon as you buy it, and when you're done reading one "book"? Just buy the next, no wait! (part of it is probably how i hate the feel of paper/particulary comic book paper) In my case, i read mostly manga. So that too is even better online - when the japanese version is revealed, lesser translators get to work on giving people a good idea and hints before the official translation is done too. But with the book you gotta wait a long time because after the official translaiton is done, that's still gotta be shipped over the world so you gotta wait for that too, then buy it and wait for it to be delivered.
There are some amazing webcomics on the web (or so I've heard), but nothing can beat having an actual hard copy in your hands. Speaking as someone with a dinky laptop and rarely any good internet, you don't need an internet connection, or an internet-surfing iphone or anything to read an actual comic book, nor does it matter if you have a really small screen that you can't see the whole thing on.
That said, I've always been the type to prefer the older over the newer in technology, with very few exceptions, so maybe I'm just not adapting to the times. *shrug*
I think I prefer reading webcomics due the fact there tends to be more author-reader interaction and fans don't have to worry about waiting and not knowing as much, because they're able to find ways to get at least an idea of when an update will happen.