Thanks both of you! So basically, either Decline and Fall, Sword of Honour Trilogy, Scoop or A Handful of Dust is what you two are telling me.
BP, I saw that you'd called the trilogy his other masterpiece, but then I saw Lynx-lynx thought it a little bland. That normally wouldn't stop me, but even though I love the time period I'm also a little burnt out on anything too WWI or WWII if it's too military-based, which I don't consider Brideshead Revisited (although, I do have some few like that on my tbr). I don't know how much those books resemble that but it gave me pause, along with it being a trilogy I'd be committing to as well. Given your view of it as a masterpiece though I do want to read it at some point.
Unless Decline and Fall gets a particular recommendation I suppose I don't see any need to start from the beginning with Waugh. He's an author I think I might like to read all the way through if I like the others as well as Brideshead, but there's just so much to read and so many authors I'd love to read through that I still haven't!
That leaves Scoop and A Handful of Dust if no one else replies. I can't decide right now from both of your recommendations so I'll add them both and see which strikes my fancy at the pertinent time, and the other will be the third Waugh I read. I appreciate the help; when I was looking at his oeuvre no one thing really stood out.