The Laserjet II is PCL4. The Laserjet III is PCL5. The Laserjet 4 is PCL5e. There is backwards compatibility all the way back to PCL1 with very few exceptions.
http://www.csgnetwork.com/hppclhist.html
With that in mind, I think I'd choose LJ4 emulation, it may perform a bit better in Windows.