Both Chunky and CDisplayEx on Android have a reader option where single pages fit to both the height and width of the screen and landscape double pages fill the height of the screen and can be scrolled to the right by tapping or swiping to see the second page.
The Fill Screen option on panels comes close, but if the comic is wider or taller than the aspect ratio of the screen it means having to tap the screen twice for each page turn because the first tap scrolls you down or across first.
