I go here quite often for lunch because it is surprisingly quiet for bang in the middle of London. There are always plenty of free comfy arm chairs up on the mezzanine floor which is darkly lit, perfect for relaxing with a book and a cup of great coffee. Compare this to suffocatingly busy Starbucks or Pret down the road and it's an easy winner.
Newly opened, this branch of Artigiano is a big space with a mezzanine floor, perfect for watching the busy New Oxford Street world go by. Highly recommend the coffee from Origin Coffee Roasters and there's a good selection of cakes and freshly prepared rolls. It was rather quiet on the Thursday afternoon when I visited and seemed to lack atmosphere, but this may be quite different during busy lunchtimes and in the evening. Worth keeping an eye on.