Germany

StudioCanal Germany 4K is better than Shout! Factory. Plaion are StudioCanal’s distributor in Germany and one of their representatives revealed in a Germany forum that StudioCanal hired LSP to do the encode.

StudioCanal Germany 4K got a proper 5.1 mix instead of the Shout! Factory upmix

Germany Blu-ray and Criterion Paramount no difference, just get Criterion https://caps-a-holic.com/c.php?d1=11014&d2=10022&c=4022

Germany Blu-ray has English audio 

Germany Blu-ray is part of a 3-film box set like the Criterion but by StudioCanal 

Both 88 Films and Germany Capelight are superior to the Shout! Factory in HDR10 but their FEL layer may even things out. Objectively, the Capelight looks best as they avoided the chroma blocking that’s visible in 88’s disc but they in turn included an Atmos mix. I have the Shout! Factory, love how it looks and the 4K transfer is spectacular. https://slow.pics/c/vPmFQSAH

Shout! Factory has the exclusive The Beauty of the Baud and the You Can't Stop Us All featurettes.

UK Blu-ray is censored

German release from Plaion has better grading and encode than the US Vinegar Syndrome releases.

Both UHDs come with Italian and English audio, as well as English subtitles.

Turbine Germany 4K Blu-ray is disappointing review

Both will look identical in motion but the Turbine looks marginally better due to a higher bitrate allocation by each cut being given its own disc, whereas Arrow had FiM seamlessly branch the two onto one. However, Arrow has both cuts in Open Matte (on Blu-Ray) and corrected the opening Universal logo's aspect ratio. https://slow.pics/c/McvVcYDG

Germany Turbine 4K Blu-ray > US Kino Lorber 4K Blu-ray

comparison between the Turbine and Kino grades. The former is director-supervised.

The Kino Lorber 4K Blu-ray was recalled shortly after inital releases for unknown reasons.

Fan preservation is likely better quality.

The 2011 Lionsgate Blu-ray is incredibly poor for every Original Trilogy film; older processed older DVD-era masters with heavy use of DNR, sharpening and edge enhancement with a really dull color grade. The 4K Blu-ray is miles better. The DTS-HD 5.1 across all three films appears to be the same on both the Blu-ray and 4K Blu-ray, and they appear to be the untouched theatrical 5.1 mixes. 

The Uncut version has more violence: https://www.movie-censorship.com/report.php?ID=256325

Germany StudioCanal 4K Blu-ray slightly better

Germany StudioCanal 4K Blu-ray has best encoding. France Potemkine and Criterion UHDs slightly worse.

Kino Lorber 4K Blu-ray or Germany Capelight 4K Blu-ray? see caps by The HDR Dissector

Arrow Blu-ray has the most extras

Lionsgate Limited 4K Blu-ray see caps. Much better contrast and grain exposure but the grade is a bit questionable as it skews heavily towards magenta in some caps and the encode looks low-pass filtered.

Lionsgate and the upcoming Imprint have the same discs.

Lionsgate 4K Blu-ray encoded the "Original 5.1" as lossy Dolby Digital, which is very different from the AC3 on the original DVD.  This new "Original 5.1" may in fact be a downmix of the Atmos track.  FWIW, the original DVD AC3 still sounds very good.