Probably reiterating what others have said, but...
THE EVIL DEAD: The Book of the Dead (as other folks have said) is the way to go, mainly because of an excellent transfer and an awesome DTS ES track. However, it's framed at 1.85:1, which allegedly is the director's choice although all versions previous have always been 4:3, with the movie projected at 1.85:1 for theatrical showings. The Elite has the 4:3 version, and a lighter transfer, plus two great commentary tracks, but those are repeated on The Book of the Dead. Because of the framing issue, I have both but if you're going for one, go for The Book of the Dead.
EVIL DEAD II: The Anchor Bay SE is great. Great commentary, a fun featurette and a great THX'd 5.1 track. The tin is awkward, and if I remember correctly OOP, so the Amaray is the way to go. Be wary though: AB also did an earlier version which was bare and shitty, so if you see a version with the famous creepy skull, avoid. The one you should be going for has the painted art from the UK theatrical poster.
ARMY OF DARKNESS: There's tons of versions, but it all depends. If you want both the director's cut and the theatrical edition, go for the Boomstick Edition, which is a repackage of the original 2-disc LE that Anchor Bay put out. It's got some cool extra stuff, and a decent commentary, however, the transfer on the director's cut sucks. If you're interested in having a perfect director's cut, the MGM disc from Region 3 contains the commentary and some extras, plus a perfect transfer of the director's cut, and as far as I know is the only way to get that good transfer on DVD. The title Bruce Campbell Vs. Army of Darkness is just a retitle Anchor Bay used on the second reissue of the second disc of the 2-disc LE (being the director's cut), being the one with the imitation brown bag cover. It's just a title to align it with the film (as BCvAOD is the film's on-screen title), but means nothing in terms of anything extra.
Hope this helps.