As an alternative to DEC LPS, one other possibility I'm considering for
 a perfect PostScript printer would be an original Apple LaserWriter. 
I would avoid the very first Laserwriter. It uses a CX engine, which is
very solid and well made, but getting toner cartridges for it is
non-trivial.
I use an Laserwriter II NT (SX engine). I'll make a few comments on that
below.
  But since I'm NULL in apples, I need some help.
 1. Are all LaserWriters 100% pure PostScript printers, speaking nothing
 but PS?  I know the very original one was, but I'm not sure about whatever
 happened later and whatever they make now. 
The LW II NT has a DIablo 630  emulation mode (!), selected by DIP
switches. It's fairly useless. Apart from that, all it understands is
Postscript.
  3. The original LaserWriter had a serial port.  But
given the assault on
 serial ports coming from all directions, I don't expect the current ones
 to have one, or do they?  When was the last LaserWriter made with a serial 
The LW II NT has a real RS232 port on a DB25 connector. It also has
Localtalk on the standard 8 pin miniDIN (this is technically a serial
port, but probably not what you meant). There is no parallel port.
  port?  Was there ever a LaserWriter new enough to
support duplex printing
 but old enough to have a serial port?
 4. Are LaserWriter serial ports standard EIA-232 DB25 or something Apple
 proprietary?  If the latter, what kind of adapter would I need to make? 
It is DB25, buit the pinout is a little odd (IIRC the ready signal is on
pin 11, I can check the schematics if you end up with one). Wiring the
cable took a few minutes.
-tony