I found this a particularly tough category to rank (of those I had read), and I'm also aware that my own tastes are particularly out of sync with those of other voters here, so it may not matter that much. For what it's worth my order of preference is:
4) Locke & Key Volume 5: Clockworks, written by Joe Hill, illustrated by Gabriel Rodriguez – a brilliant opening episode, but much of the rest depended rather on the reader having more knowledge of previous volumes of the series than I had. No doubt some voters will vote for the series as a whole; the previous volume came third last year, behind Digger and Fables vol 15.
3) Saga, Volume One, written by Brian K. Vaughn, illustrated by Fiona Staples. As noted earlier today, I loved the art here, but was less overwhelmed by the story.
2) Grandville Bête Noire, written and illustrated by Bryan Talbot. Witty and artistic, and a very tough choice as to whether I should put this top; I might yet change my mind.
1) Saucer Country, Volume 1: Run, written by Paul Cornell, illustrated by Ryan Kelly, Jimmy Broxton and Goran Sudžuka. A story about UFOs and an American presidential campaign: perhaps not as High Art as Talbot, but tickles own peculiar tastes a good deal more, so gets my top vote. Probably.
This is a good list; it was in no way a chore to read any of these.
See also: Best Novel | Best Novella | Best Novelette | Best Short Story | Best Related Work | Best Dramatic Presentation (Short Form)