Impossible to say since there are a lot of subjective factors that will dictate our choice.
Where we were raised, the musical environment will be the first factor I think; while we have nice English sample sets available, I personally don't get excited about them because I never heard a real Willis, on the other hand, while I was a teen, I had a few records where I discovered the Cavaillé-Coll sound... so I love a nice CC sample set.
With time, I learned to love the OAM sample set... not used to historical temperament, at first I didn't like it the way pieces sounded... being used to Equal 440, my ears often "twisted"... now I can't get enough of it; my music (cd/streaming) collection now has a ton of music recorded on historical instruments with "beautiful temperament". In Quebec city we havea nice little 1 manual organ
, built according to the specification of the original organ (early 18th century). I don't recall its temperament, but I just love it and go to ever concert held there now.
There are some sets that I own that I like more or less... then a professional organist comes to my place and play it, registering with beautiful tones, playing with the right articulation and suddenly discover an incredible instrument. Some instruments/sample sets are harder to play, to make it sound nice... dryer instruments are harder to play, so amateur will usually like wetter one since it covers the lack or incorrect articulation, little mistakes etc.
Best sound, quality, realism is quite relative I think; in the early 2000' while I was hanging on some photography forum, we were discussing pixels, contrast, speed, saturation... forgetting the basic of any good photography...a good subject and a good technique.
For us using Hauptwerk, we should enjoy more what we have, what we like personally instead of searching for THE sample set, getting more speakers, more powerful computer... simply enjoy what we have and try to expand our musical horizon... Hauptwerk is a beautiful "travel machine", where we can experiment various aesthetic, era and repertoire.
Because of my musical culture, environment and personal curiosity, I probably have preferences that can be quite different than yours.
Another 2 cents worth