Ok, I've realised this poll requires a bit of ... let's say "historical imagination"
So using like photos, video recordings, facts that are known about the tour, audio bootlegs of soundboards and audience recordings and officially released tracks to inform your decision, you can pick any tour.
I went with the And Then There Were Three Tour because of the incredible stage presentation with the lights and mirrors (in my opinion their best looking stage), one of the best and most surprising setlists with deep cuts from ATTWT, all of which are the definitive versions and eclipse the studio versions majorly, the fact that they brought back Fountain of Salmacis (probably my all time favourite Genesis song), Ripples, the full Cinema Show. Now that I think about it did we ever get such a variety of 'old' songs on any other tour, I mean they did Dancing With The Moonlit Knight, The Lamb Lies Down On Broadway, The Musical Box Closing and Apocalypse in 9/8 at least one show each.
Also it has Tony's best keyboard rig by a mile, we got the start of polysynths with the Polymoog, the first use of the Yamaha CP70 electric grand piano as well as old favourites like the Hammond and Mellotron. Oh, and the crowning glory, they casually toured with an ARP 2600 as Tony's main lead synth. Tony's rig alone puts a lot of the versions of songs into the A+ tier.
Also I think I like Phil's voice on this tour the best. We still had his beautiful soft tones on songs like Ripples, but he still had more power on the songs that required it. Like on the 76 and 77 his voice seemed to get blown out sometimes when he was trying for those heavier sections. And, not yet as raspy as the later 80's which I'm not huge on. Chester and Mike were on fire too. I have to admit also that I really like Daryl and Mike's guitar playing on a lot of the songs. The way they played on this really filled out the sound and didn't leave it all for Tony to do.