36-38mm watches are generally my favorites. Even a 42mm Omega or Rolex looks and feels too big on my 6.8" wrist.
Yet I own several 47mm Panerais. My wife and friends ask why I choose to wear a clock on my wrist! Part of the reason is that PAMs were designed to be big, for legibility underwater. Another part is that the simple dials of two-handers like the 249, 587, and 721 somehow compensate (somewhat) for their large size. The 249 and 721, for example, have simple blue hands that only shine from certain angles. The 587 has gold hands but a nice symmetry that gives it a lower key, classic appearance. Other big, modern watches can be flashy while a large Panerai often makes think fantasy or whimsy instead of luxury or affluence.
No argument on comfort though. My 36mm 114270 Explorer or slightly larger Hamilton Khaki Field or Omega Railmaster can be worn all day without discomfort. A 40mm Sub feels larger and heavier. And the big PAMs, even more so. Yet today I'm wearing the relatively trim 249 and it's pretty darn comfortable -- for a wrist clock ;-)