Christopher Ecclestone then David Tennant. They were both brilliant but Christopher Ecclestone played it a bit more angsty which I liked.
Part of the reason I never took to Matt Smith, his doctor just felt too young and silly, he didn't seem to capture the deeper darker side of being a timelord which the other two did while still providing comic moments.
For me it is Jon Pertwee as he was the Doctor I remember most from growing up with the series (I was too young to remember Troughton in detail). Of the recent revival, I was sorry that Ecclestone only did the one series as I liked him. Paul McGann didn't get enough exposure on TV, but the Big Finish/BBC Radio 4 Extra audio dramas have served his Doctor well.