I: Fall of the Jedi Fanedit – As this is the only one of the prequels where I really can’t stand the childish stuff and FOTJ does a good job of chopping that out.
II: Official 2011 BD
III: Official 2011 BD
IV: Depends. Sometimes 2011 BD, sometimes whatever the latest “best” is of the unaltered versions. I actually don’t mind most of the changes but I like to see the original cinematography and so forth from time to time and so I watch the best unofficial of the unaltered originals (lately TN Silver Screen transfers).
V: Harmy despecialized and 2011 BD depending - Same reasons as above
VI: 2011 BD and Grindhouse 35mm - Same as above
VII: 2D BD; I may prefer a fanedit in the future if someone decides to throw together a fanedit with deleted scenes intelligently inserted for an unofficial “Extended Edition”

Rogue One: N/A - Have not seen yet (I no longer go to theaters) but I intend to watch 2D BD once available.

I don’t care for 3D, so if any 3D versions exist of the above I am referring to 2D if not stated.

My preferences are based solely on visual aspects as I cannot really compare the auditory differences – I only own a 2.0 sound system.

When I own a 4K display some day and when these are all re-released on UHD-BD (“4K Blu-ray”) then I’ll certainly check those out if and only if reviews state that they have more detail over the BD versions. As 4K versions do not necessarily have more detail due to a botched transfer and/or poor source media. There’s also other issues such as bitrate starvation that sometimes makes lower resolution mass media versions superior if using a decent scaler to rescale the output to your display’s native resolution (such as an HTPC with madVR’s various scalers). Oh and of course, for the PT many of the CGI models would likely need to be redone to be appropriate for 2160p/4K unless they intend to hawk out an “upscale” (like many early BD releases of movies were just upscales of existing 480-720p transfers to digital).