What should I read first?

[Silver]

I got the Grey Knights Omnibus, and the Inquisitor Omnibus sitting on the shelf at home. Having recently dabbed into the Ordo Malleus, I was wondering which of the two you'd suggest I read first? Or is it completely irrelevant?

Cheers,
-Silver

[Wakim]

Seeing how the new codex raped the whole grey knights, inquisiton and part of the imperial fluff... i'm pretty sure it's completly irrelevent with which you start as they're not-so-canon anymore.

PS If you're into 40k book, get yourself a copy of Xenology.

[Anne Marie]

Start with the Inquisitor omnibus. That way, you can at least get a good inside view of how the Inquisition works amongst itself and others. The Grey Knights are a bit different since they're only tied to the Ordo Malleus, but the Grey Knights omnibus was written well before the Grey Knights were... unfortunately updated. They maintain their purity in some sense of the word through the stories.