I definitely have my own personal pantheon of literary luminaries, but it's hard to rank one above the other, especially since styles often differ. Among the classics I really love Eça de Queirós, Italo Calvino, Dostoyevsky.
For a good laugh I feel comfortable turning to the likes of Tom Sharpe (the first couple of books in the Wilt series and Porterhouse Blue are among my top comedy novels). If I want to tone down on the slapstick and go for a bit of sarcasm, David Lodge is also a safe pick. Max Barry also has interesting, humourous views on the modern world.
If I want something light, the action-filled historical novels of Valerio Massimo Manfredi or Ket Follet usually scratch that itch.
When it comes to top tier literature, something to challenge me a bit more while still accessible, Umberto Eco and José Saramago are my favourites. Been getting a lot into Margaret Atwood, Hilary Mantel and Jonathan Franzen lately.
Umberto Eco is also among my favourites for non-fiction, along with Simon Schama and Jared Diamond.
Also, if you count comics as literature, then Alan Moore, Brian K. Vaughan and Lewis Trondheim reign supreme.