What's the difference between these drivers?:
PCL6 (or Printer Command Language, Level 6), PS (or PostScript) and PPD (or PostScript Printer Description) are all ways a printer can "communicate" with your PC via it's driver and define how the page will be "drawn" by the printer (text or otherwise).
Which one should I use for my installation? Should I just check all of them?:
You'll have to refer to the manual for the specific printer you are installing to see which driver to specifically use when printing; although installing "all" of them won't "hurt" anything, you'll just need to be sure to choose the correct driver when using the printer.
XPS or the XML Paper Specification is an 'open' driver standard made famous via Microsoft's XPS "print driver". It's another way to "communicate" to the printer (if the printer "understands" XPS).
If you install the Microsoft XPS viewer (and subsequent XPS drivers), it will give you a "virtual printer" that you can then print to file (as it would be printed on page). You can view the .xps files with an XPS viewer and physically print them. I personally use XPS on my Windows machines when I might want a printout of some "important" information that I can physically print later (without having to waste paper at the time or if my network printer is offline at the moment).
In the end, you should be able to select "all" and Windows and the printer can determine which driver would be the best to use (or at a minimum you can uninstall the incorrect driver).
Hope that helps.