Hmmm...ive heard all but Up The Downstair and Stupid Dream now, making picking a fav very hard...I love very personal psych-pop of Lightbulb Sun, but I also love dark-rock of In Absentia. TSMS is a full on prog-feast, but Voyage 34 is full of wonderous ambient soundscapes...
I think im going to have to go with Deadwing. This album should never be underrated, its marriage of prog, hard rock, pop, psych and ambience so tightly done and refreshing that it can be listened to over and over again, without growing stale (except for Halo; the album could've done without that song). The energy and confidence it brims with put a smile on my face every time. Basically, Deadwing feels like the way forward, and as great as their past works have been, theres just something enticing about Deadwing's newness.