I was just perusing the archives and noticed nobody had replied to you about this RT, so here you go, some five months later.
Basically, with "Evil Dead" the best version to get if you just want the movie itself is the single disc Anchor Bay SE released in 2002. It has all the extras included on the "Book of the Dead" set (although some of them aren't accessible through the menu; you have to manually enter the title numbers; if you'd like, I'll do some digging to see if I can find the info on how to access them) but at about a third of the original retail price. I see this at Wal-Mart on a regular basis for just under 15 dollars. If I'm not mistaken, the BOTD version is out of print now and the SE has all the material it has anyway, so unless you're wanting the packaging (which admittedly, is extremely cool), I'd say to go for the 15 dollar SE.
As you noted, there's only one version of Evil Dead II available at this point and it's actually quite good. The transfer is the best I've ever seen the film look and the commentary is easily one of the funniest and most entertaining I've ever heard on any DVD. This one is fairly cheap these days as well, and is well worth picking up. It's my favorite of the three films and my favorite of all the DVDs done of the trilogy.
"Army of Darkness" is a film that I'm still not as fond of as the other two. That said, the best version of the film can be found on the two-disc "Boomstick" version. It is actually just a repackaging of the Anchor Bay THX version and the "Bootleg" (also released previously as the "Director's Cut") version in one two-disc package. Disc one is the theatrical version and only has a trailer, the alternate "future" ending, and a short (30 minute) documentary on the making of the film. The second disc (the "Bootleg"/"Director's Cut") has a version of the film that is about 15 minutes longer, a commentary track with Bruce, Sam, and Ivan Raimi, and a few deleted scenes. If you get the "Boomstick" version, you've got everything that has been released before. Anchor Bay just keeps changing the names and artwork for reissues and what not.
That being said, the transfer on the "Bootleg"/"Director's Cut" disc is horrible at times. They used some really dodgy sources (often video dailies) for some of the added scenes and it looks like a tenth generation bootleg VHS copy at times. Plus, and this is just my opinion, the film works better with the S-Mart ending and at the shorter theatrical run time. Your mileage may vary, though.
AOD's European distributor actually released a DVD of the Director's Cut with a pristine transfer (apparently they had the original source material on film whereas AB/Universal US didn't), so with AB's history of releasing this title over and over, it wouldn't surprise me if yet another version of AOD is coming in the next few years with the improved transfer.
So, to sum up, if you're keeping score, here's how I would go with the discs:
Evil Dead: Anchor Bay SE (2002) in keepcase
Evil Dead II: Anchor Bay SE (2001) in keepcase
Army of Darkness: Anchor Bay Boomstick Edition (2003)
Hope that helps you out and sorry it was so late in coming!