Just to let you know first, I also have a thread/poll on the Escalation series alone, but this thread is about all the Halo comics in general.
So which comic book or series did you like the most?
Escalation, most definitely. Though Bloodlines is shortly after. Not just because of recent events, I have always loved Bloodlines, I got so attached to Otto, Victor, and Margaret. Trying to detach myself a bit now. Helljumpers would be number three. I really enjoyed exploring Dutch and Romeo. (I have read most if not all the Halo comics and enjoyed all. 
)
‘The Fall of Reach’ comic adaptation was my favorite. The art was gritty but solid, it stuck pretty close to the book, and all the Spartan-II action didn’t disappoint.
Escalation for sure. I’m currently waiting for issues 7 and 8 to arrive in the mail.
My favorite one is the Graphic Novel.
Simply because of the amazing story about Rtas 'Vadum and Johnson’s short survival story. The art style was fitting enough for Halo, which I can’t say about Escalation.
While I still enjoy Escalation, it has its flaws.