(1) The Lamb
(2) Selling England
(3) Foxtrot
I like a lot of Phil Collins-era Genesis, but for me, the Gabriel era is the best.
Some criticize Gabriel for the sometimes opaque, dense plot of the Lamb, but name a rock concept album that doesn't have a confusing plot or theme. (I love Quadrophenia, but I don't know what the hell is going on half the time.) The Lamb can be simplified as a character on a journey of self-discovery in NYC. Even PG said that the Lamb at its core isn't that complicated. "The Carpet Crawlers" is still an amazing track, as are many others here. "Anyway" would get my nod as an underrated number.
It's a coin flip for me between Selling England and Foxtrot. I'm not a huge fan of "The Battle of Epping Forest," but the rest of the album is perfect. Supper's Ready, IMO, is still the best piece of music Genesis has ever produced. The plot of "Get 'Em Out By Friday" is hilarious.
I started to really love music as a kid in the prehistoric year of 1981. That's probably why Abacab was always my favorite from the Phil era. I soon fell in love with PG's solo and Genesis work, but more so the solo stuff.
I also liked "Genesis" a lot when it was first released. Great memories from that era of pop music, including the late '70s.