Porcupine Tree.

Doesn't matter. All quality. Just remember that the earliest albums were more psychadelic, the mid-era albums more a pop orientation (though merged with psych and rock), and the more recent bringing out the rock stylings (though not forgetting earlier PT).

If you want album by album info, just say. One thing PT fans love to do is spend hours debating which is their best, and will be happy to jump to the defence of their fav.

ps. Deadwing.
 
I only have three albums from PT but all are great, and have a sound to their own.

Deadwing
In Absentia
Up the Downstair

All are good and I suggest you get them.