Formatting: I uh...I don't care honestly. Left to right, right to left, as long as I can read it then I'm fine with it. The problem comes when I go from reading manga to comics and vice versa, I get confused with the formatting for a second. Kinda frustrating.
Though out of the two I'd have to say I prefer manga. Why? Simply because I like when I pick up a manga it isn't a rehash of the same character by a different writer. I go to a comic store and there's a million Superman comics, each one by different writers in which the stories have no relevance or connection to one another at all (I'm of course basing this off of DC and Marvel, not any other comic publishers). Whereas with manga I don't get eighty different DBZ manga that has no connection to one another whatsoever.
I'm not bashing DC or Marvel for that though, I understand why it's done, but it gets pretty boring reading about the same character over and over when each story has no relevance to one another. That doesn't mean I have zero problems with manga though, but that's a topic for another day. This is just my reasoning for enjoying comics less. Erm, however, if I wanted to read something then books are my choice instead of manga and comics like Jorick said.