I think Good Omens, cowritten with Terry Pratchett, is funniest, the Anansi Boys the best (so far), and fairly short, too, but if we're choosing Davis & Evanovich's first books, then I think it should be "Neverwhere"; not the first thing he's written, but the first novel.

I'll be okey with Davis, as she deals ancient Rome... FYI, Gaiman writes about ancient myths/gods etc, sometimes in a modern world or fantasy environment...


PS: I'll pass this time, if you want to read Evanovich; I tried to start "One for the Money", but couldn't make myself to like any of the characters, and for me that's one of the basic rules in reading a book; you have to be able to care about at least one person in it. Or maybe I just hate bounty hunters? ;P