Comics by comiXology is ranked #3 in Apple’s chart of the top grossing iPad apps of 2012, according to Inside Mobile Apps.  It trailed only DragonVale and Slotmania HD, two heavily addictive free-to-play games, and led productivity apps Pages and Quickoffice Pro HD, and games Slotmania, Kingdoms of Camelot: Battle for the North, Modern War, Mystery Manor: Hidden Adventure HD, and Clash of Clans.  No other comics apps charted in the Top 10. 
The Comics app has been charting strong since the fall of 2011, when a new version and the rapid expansion of new releases began pushing it to the top of the charts (see "comiXology Charts at #2").
No comics apps charted in the top ten grossing iPhone apps.
--Disclosure: ICv2 has a business relationship with comiXology as a representative for its Retailer Tools; ICv2 CEO Milton Griepp also serves on the board of comiXology.