Which of these will be released first?

Diablo III I suppose.

I don't really know about A, but a Halo movie isn't even in production. That's automatic exclusion. Diablo III, easily.

The Halo movie no longer exist so that is off, and I don't listen to Dr Dre so that might as well not exist :P so default!

Just 1 real option here, least for me,  D3

well, seeing the quality the Halo script usually have i guess they can make a Halo movie within a year or two, Diablo 3 will be delayed and we probably wont see it until late 2012 or 2013, and i dont care about Dr. Dre.
So aslong as they start making a Halo movie this year, it should be the first to hit the market

Diablo III. The Halo movie isn't in production and although it could conceivably get picked up by someone it'd still take ages to make.