Hardback and sweet as sugar.
That's the one I got for my birthday this year, and just recently finished. It is indeed pretty awesome.
The only stuff it's lacking are the "collaborations," like "Two Black Bottles" and "Horror at Martin's Beach."
I think there are still a lot of copyright issues with the collaborations. It used to be 75 years, no questions. Until Disney's stuff started getting to the date and now it seems the laws are being rewritten and being more complicated. HPL had no direct descendants so it makes things a bit more cut and dry.
So I've heard. I really don't know a thing about law.