I agree: for me too the title of best KQ adventure is an issue between KQ3 and KQVI. My best remains KQ3, but I admit in advance that I am partial to the amazing group of AGI adventures from KQ3 (included) onwards.
During those times (Ken may confirm or deny of course) it seems to me that there was the perfect combination of fresh ideas (guaranteeing new topics and plot), tight programming groups (in real control of the whole project) and simplicity + stability of the AGI system (known well it allowed itself to be exploited to the max and programmers remained focus on the core of the adventure and on making it flow). It is not by chance to me that in those times besides KQ3 also the first Leisure Suit Larry came out, SQI and II, the innovative PQI, the beautiful and historically accurate Gold Rush…
Of course, the later evolutions were needed.
Ken and Roberta were right in pushing for the technological and interface advances: they were their vision (a sort of interactive movie) and also businesswise the only way to proceed (proof be that old Sierra lasted much longer than Infocom which remained tied to the text and than other less innovative competitors).
Among the adventures that came after AGI there were for sure some great ones too, and KQ VI is one of the best. Indeed very good.
I just finished replaying it and, while I did not like a lot the very first part, almost all the rest is great. Plot is long and with depth and it is a rare case of adventure with truly multiple endings, which adds a huge lot to it. Well done Roberta !
I also agree on the judgement on Gabriel Knight.
Personally, I think all three the GK are truly amazing. Each with its different aspects and tecnique, represents a perfect piece of what to me can be considered the best Sierra series as a whole. While the other series are probabily even more highly remembered by many, but they include a combination of number one adventures, but also some that are good but not perfect and a few that are less accurate. GK instead has three adventures only in the series, but all great to me. Jane Jensen is in fact a good example of a Sierra writer who maintained plot above all, even in truly new systems, and you can easily tell. If I am not mistaken, she was coming from a contribution to… KQ VI, and for sure she was of great support to Roberta !!!
Well to close, above all, I will always thank Ken and Roberta for the great old Sierra times ! As said, first of all I’ll never forget the good old AGI ones, but each Sierra adventure I played gave me a lot of enjoyment I will never forget.