I am biased because I am the editor and publisher of
Elegant Complexity, but let me tell you what I know. Elegant Complexity is modeled after a guide to Ulysses called The Bloomsday Book (by Harry Blamires). It takes each section of the novel, provides a summary, a discussion about the themes and characters, and a lot of reference material in the appendix. It is not really literary criticism. In fact, the author, Carlisle, is a theater professor, not an English professor. I think one of the coolest features of EC is the map of Enfield Tennis Academy. The description of the place can be somewhat hard to follow in the novel and I think it's ultra helpful to see a visual representation of it.
I am also a fan of the Continuum guide by Stephen Burn. Burn's guide follows the Continuum series format and is rather short (96 pages). It includes a helpful chronology and sections on the novel's critical reception and key plot points. By contrast, Elegant Complexity is 512 pages long. There is one other "Reader's Companion" out there (edited by Dowling and Bell) that I would not recommend because it includes many errors that could confuse the first-time reader.
Here is a family tree of the Incandenza family from Elegant Complexity:
http://www.flickr.com/photos/mbb/2219381416/