Neo Psychedelia: from On the Sunday of Life to Signify
Prog with Brit Pop flavour: Stupid Dream and Lighbulb Sun
Prog with Metal flavour: In absentia to The Incident
Again, it depends on your taste but if i have to select one record from each era, that would be
Signify from 1996. Good production and dark sound and less derivative than their previous efforts (I wouldn't skip Up the Downstair too)
Lighbulb Sun from 2000: the best in songwriting with a good mixture of pop (first half) and prog (a couple of long songs in the end)
Fear of the Blank Planet: hard but modern prog rock with Alex Lifeson and Robert Fripp as guests musician. It's also pretty diverse. My favourite
Also, I recommend you Voyage 34: The Trip which in fact is more like an experiment rather than a true album as most of the pieces were recorded (or mixed) through the years. It's instrumental, really trippy and provides a good mixtures of modern electronica, ambient and prog rock.
Regarding SW solo career, incredibly, I like it more than PT. I think it's because it's more diverse and less style compact, with better production and chops and emotional component that is mostly absent on PT. I would recommend any of the 5 albums (4 proper and 1 EP) as any of them is attractive
Insurgentes from 2008 is the most PT sounding but pretty diverse, you havev everything from Krautrock, Ambient, Shoegaze, etc.
Grace from Drowning from 2011: double (although 82 mins only) with a lot of jazz influences
The raven that refused to sing from 2013: very retro prog sounding and co produced with Alan Parsons. The title track is my favourite piece from SW. Supreme
Hand. Cannot. Erase from 2015 returns to the diverse approach with a couple of incredible songs and a very emotional approach about people isolation in modern world (nothing new in fact but again, what is new these days)
4 1/2 was published in 2016 and compiles unreleased songs from previous records' sessions. Good although not a MUST
Hope this helps. Sorry if message too long but what can I do, I love SW (although never care about his remixing works)