Ok...i'll pitch in. I'm more than qualified to throw some Hellblazer recommendations at you as i've read (and own) every issue published thus far. At it's best it's been my most loved monthly title and at it's worst i've come withing a hair's breadth of dropping it from my pull list. Here's my thoughts on the various writers who have sculpted the world of John Constantine.
1. Alan Moore - He created Constantine in the pages of Swamp Thing but the character was a lot more enigmatic in those days. A mystery man who would pop in and out of the storylines and manipulate events towards a resolution that only he could see. It was a great introduction to the character and he proved so popular that DC greenlit a solo book. Hellblazer was born.
2. Jamie Delano - I'm not certain whether DC actually asked Moore if he wanted to take on the task of writing Hellblazer but if they did he must have knocked them back. Probably didn't want to get tied into another monthly title that he had no ownership of. So fellow brit Jamie Delano took the job. Faced with the task of fleshing out the character of John Constantine who at that point was little more than a cypher he succeeded 100%. His 39 issue run on the title (ignoring a two parter by Grant Morrison that surely must have been inspired by The Wicker Man and a wonderfully touching one-shot by Neil Gaiman) remains one of the highpoints in Hellblazers epic run. It got a little bit muddled and mystical towards the end but I loved every page of it.
3. Garth Ennis - Next up to bat was the great Garth Ennis. His take on Constantine is considered by many to be the comics high watermark of quality. And I agree (but only just). His run on the title saw Constantine facing off against vampires, royalty, his own mortality and the nefarious hordes of hell themselves. It also saw the character find love with a beautiful dark haired Irish lass and this was the storyline that provided the heart of his run. There are some supremely moving moments as his relationship falls apart (inevitable given his line of work) and in particular I was blown away by the heartfelt honesty of the issue where John says goodbye to Kit. Absolutely devastating.
I'll cover the rest of the Hellblazer writers tomorrow night. Short on time this evening.