I'm going to list my top 5 and then pick my favorite out of those. Here's mine:
-Green Arrown Deluxe Edition by Lemire/Sorrentino--an outstanding new take on GA, with a whole new introduction of mythos and cast of characters. Sorrentino's art is amazing and Lemire's story is so fantastic and I'm not even a GA fan. It's one of the few books this past year that I absolutely HATED to put down. I just wanted to keep reading it and reading it all in one sitting, but I just couldn't. They totally knocked it out of the park. I also love how the actual cover is different than the dusk jacket too.
-Lazarus Deluxe Edition--Beautifully drawn by Lark with a great concept and fresh story by Rucka. I was sucked in from the very first issue. Just a superb book.
-East of West - The Apocalypse Year One Deluxe Edition--Hickman's writing is second to none. He's my current favorite writer and this book is like nothing I've ever read before. Part sci-fi, part spaghetti western, part apocalyptic. This one has it all and the artwork fits the book perfectly by Dragotta.
-Five Ghosts--I felt like I was reading Indiana Jones with super powers. The art felt like a throwback to the John Buscema/Romita Sr. days and it's written quite well by Barbiere.
-The Multiversity Deluxe Edition--What can you say about this book? It's written by Morrison with artwork by various top talent in today's comic book world, most notable Ivan Reis. It takes you everywhere and back again.
Basically, all of the above are all amazing and I could pick any one of them and be perfectly fine with it, however it comes down to THE best of collection of 2015:
It's very, VERY close but I have to go with East of West. It's a truly magnificent book. I absolutely love Hickman's writing and Dragotta's artwork fits the book so well, it's a perfect match. It has everything you want in a comic--a well crafted and woven story with sweet eye candy art and a cool cast of characters. I can't wait to get the next book in my hands.