So far, Kerr's are the definite best edit. The most important characteristic is the somewhat successful separation of the storylines according to how Tolkien set them up in the books. It adds particular resonance to scenes where Gandalf, Pippin, Aragorn are speculating as to the fate of the Ringbearer and the whole mechanic of misinformation and manipulation of the Enemy through the Palantir, ultimately paying off with the bleak Mouth of Sauron scene. In doing so, it automatically creates much more depth and tension as the viewer experiences the narrative concurrently with the POV of the characters on screen rather than assuming an omniscient position, knowing what is going on rather than speculating and feeling what the companions are.
Secondly, it removes a huge amount of misplaced, jarring comic-relief and storylines (Arwen's life tied to the ring? Really Jackson? Aragorn falling off the cliff, etc.) making for a tighter, more serious, and thrilling narrative.
Lastly, the edit tries to rectify or mitigate some of the awful characterization invented by the original screenwriters. Not particularly successful, but you have to consider the source material the editor had to work with.
The edit, however, has its particular flaws. The deus ex machina of the dead army is retained. Some stuff is awkward, the reworked scene of Frodo's dismissal of Sam didn't work too well, neither did their parting from Faramir. Some glaring, though possibly irremediable errors remain, such as the disappearance of the horses at the Black Gate. The 6 movies could be recut and resequenced into 5 for a superior cinematic experience, though it goes contrary to the other's "book cut" intent.
Kerr's edit represent a barebones, entry-level edit that attempts to make the Lord of the Rings movies more faithful to the books. However, I could not help but feel that there is SO MUCH more that could be done.
I have yet to see the Feanor edits, but they look promising, particularly some of the visual effects shots that I am quite interested in seeing (ex: Aragorn looking into the Palantir at Dunharrow). I don't have usenet, so I remain in the impossibility of viewing them at the moment. But I recommend you do and provide your own feedback!