I think Brendan O'Brien is one of the great producers, who along with Rick Rubin, is awesome at not having a particular production style, and all the records they do, even within the same band, sound different.
I think SLDD sounds the best to me. I appreciate the attitude of wanting an album to sound raw, but I think there is a delicate balance between that, and making a piece of art, like an album. First, if you watch the MTV Rockumentary, you can hear Eric Kretz tell us that Tiny Music is actually a much more raw album than Purple.
When making art in the form of an album, I think it is okay to create something than may not be able to be 100% recreated live. That is one of the things I have liked about STP, and one reason you know the songs are great--they make them sound amazing on record, and then live, they are turned into these raw songs that expose either the attitude, the groove, and/or the melody.
As far as No. 4 goes--more attention to production could've made it SO much better. The problem with the album is not everything recorded is crystal clear. Put on a set of headphones and listen to how well you can hear EVERYTHING. The time was taken to put each instrument and/or part in its best frequency range, without trampling over another's, so you can HEAR everything. Things tend to get lost on No. 4 in a muddy, murky production. I think if it sounded like SLDD, No. 4 would've come to life.