4. Josh Radnor
Josh Radnor plays Ted Mosby, the heartbeat of the whole show. The other actors may command a higher profile than Radnor but he portrays Ted with a real warmth and charisma that has been essential to the shows success. In fact I think he is better than any of the male leads on Friends. As much as I love David Schwimmer and Matthew Perry, their Friends characters became caricatures and whilst they had a Mosbian* warmth in the early seasons, that gradually ebbed away, along with the jokes, as Friends limped to its finale. Radnor is also a talented writer and director whose excellent movie Liberal Arts has just won critical acclaim.
*Mosbian is a word I have invented to describe other sitcom characters that provide a certain charisma and warmth to their particular show.