I'd probably advise starting with Emma or P&P simply because they are the most entertaining. If an Austen virgin doesn't enjoy either one of those then there's no point reading anything else she wrote. And if he or she does, well, then it's time to explore some of the lesser works in Austen's oeuvre. Persuasion is a bit of a different animal. It's her most mature and serious novel, with a depth and a subtly-crafted pathos not present in her other books. Mm, save maybe somewhat for the eldest sister in S&S.