Since both of your printers are Postscript, then the CUPS (Common Unix Print System) postscript driver that is part of OS X should work. All you need is the correct PPDs to describe the attributes of the printers to your system. PPDs for the HP Laserjet 4MP, 5MP, and 6MP are included as part of the standard Snow Leopard installation (I just found them with Spotlight set to include system files). The Applewriter 4/600 PPD is available from
Openprinting.org if you don't have a copy lying around.
You have indicated you want a workhorse printer, so I am assuming your primary interest is in printing standard size paper in black and white with no frills such as automatic duplex,
etc. Given that, choosing between the HP 4MP, 5MP, and 6MP, all else being equal, I would go with the individual printer that has printed the fewest pages in its life, and you can find that information in the menus. Printers are designed for certain life cycles, number of pages per hour, pages per month, and total life cycle. The fewer pages it has printed in its life the longer it is likely to last assuming it has not been otherwise abused or had problems.
As to the connection method, I have tried Parallel to USB cables in the past with mixed results so that might or might not work satisfactorily for you. I used an AsanteTalk box many years ago and it worked for a while. I have slept too many times since then and for the life of me I cannot remember why I had to replace it. I have no experience with the Intel box but the necessity of programming it via a PC is enough to turn me off.
Good luck!