I have bought kits from Austin Homebrew, Maltose Express, Northern Brewer and Xtreme Brewing.
For clones I'd rank Maltose as excellent, AHS and NB as very good and Xtreme as good (and probably better since it was my second brew).
For non-clones: AHS is very good, particularly when trying styles, with NB almost as good.
Caveats: I have not ordered from AHS since they were taken over by AIH. NB waited six days to process my last order, a NB non-clone kit, making me miss my first brew day.
Enter your email address to join: