My 9YO has been reading (voraciously) on an elderly Touch for about a year and a half (it broke recently and got replaced by a second hand Glo, to which he had to contribute some money).
His 7YO brother has been reading on my Aura for a few days now, and on his birthday in april it will become his property
Pictures are displayed OK (depending on how well the epub is formatted, IME) but these things are definitely not suited to reading pdf formatted comic books (zooming, panning,...) due to their low res and small screen.
If you really want the device to read comic books, you may want to buy something with a higher resolution (which does NOT necessarily equal bigger screen). I'm not going to do that though - the e-reader's for books, comics will have to be consumed some other way (maybe someday on a tablet, or just on paper).
You may want to look into the higher res 6" devices: Tolino 2 HD has 1448 x 1072 pixels (that's double the current Aura v2 resolution, and similar to the current H2O (but at a much lower price)). Higher resolution is better I think if you need to display PDF (or anything at full page size)