XTC: I had always seen English Settlement up towards the top, maybe just because it's a double.
The XTC that's made an impression on me:
White Music (fun, if insubstantial, but that's not the point)
Black Sea (starts off great but it goes off the rails later on IMO. Plus they stick the bonus tracks between the two sides as if they're '80s Fall albums; the only thing worse is Original Jazz Classics sticking the alternate take immediately following the album version.)
Skylarking (supposed masterpiece but I've always been lukewarm over it. Pretty and it has its own distinct vibe, like a Nick Drake album.)
Nonsuch (ok, I kind of like this one but it's just too much)
Also heard the Dukes of Stratosphear albums and they're... ok. I need to hear them again.