There are two Andy (that I noticed), Chambers and Smillie, Chambers is the one your talking about I'll assume. Sorry for not including him, I only wanted to include the main ones (ones that write a lot), in fact I didn't even want to include Counter and Swallow at first.

..... Counter Swallow .... If you take Ben and James together xDDD

COUNTER SWALLOOOOW (sounds like an epic attack against tyranids who try to nom nom you)

B.J Counter Swallow lol

OMG I HAVEN'T SEEN THAT!!! XDDD mwhahahha B.J. Counter swallow *rofls all over the place*

Indeed, "Benjamin James Counter Swallow!"

Abnett by far. He is ideal for me , i wish he will write a book about word bearers (aside of know no fear.) Brothers of the Snake is also the best space marine story i ever read. Incredible. And the Space Wolf comic , the best wh40k comic too.

ADB wrote the Betrayer and Aurelian which are absolutely fantastic and are about my favourite legion. Havent finished the betrayer yet but the man really understands the word bearers and im grateful for that. He depicts them exactly the way i imagine them to be. Gotta say that his night lord novels made me hate the night lords as if they were loyalists though. But who cares , his work on the word bearers is golden.

Ben Counter's Daemon World is very interesting and offers a very rare and fresh view from inside the warp. I havent read much from him though so i cant judge him from a single book.

I dont like James Swallow's works on the Blood Angels. The only loyalist legions i like are the blood angels and the iron hands so i had high hopes. Couldnt like it even when i tried.

For the rest , i havent read enough to be able to judge.

My favorite would have to be "first heretic", I think that was Abnet, but I could be mistaken.

That one was written by, Aaron Dembski - Bowden. (ADB)

My favourite 40k novel is a tough as hell decision. I've read nearly all of them, started with the Blood Angels books by James Swallow and kinda got eaten alive by the lore. I read them consistently to keep up to date with any new tidbits, new weapons, devices, characters, concepts, ideas etc., the books offer insight into the lore you dont get in codexes and rulebooks, beyond being a blast to read.

And I'm a huge Dan Abnett fan, read every one of books, absolutely adore the Eisenhorn trilogy and the Gaunts Ghosts novels.

But my absolute favourite would have to be The First Heretic by Aaron Dembski-Bowden. It outdoes Horus Rising by a sliver.