My preference changes. I would havwe voted Trick without any hesitation a few years back, but I have since re-appraised WAW.
Both are very strong albums, and in some ways WAW is more 'progressive' than ATOTT. It has more 'epic' tracks for a start, but also only has musically weak track IMO (Your own special way) Even the lyrically terrible 'All in a mouses night' is good instrumentally. The production is years ahead of its time and the performances are superb.
ATOTT, is beautifully produced and has this wonderful melancholic and mysterious feel. It also has 'Dance on a volcano' and Los Endos' Two of the greatest Genesis songs of all time
Trick wins, I guess, and gets my vote. Partly because of the respect I have for the band producing such a good album under the pressure of losing Gabriel.