Gimli, definitely. While the movies were definitely good, most characters had a predefined role for the viewer. As in, Legolas was the character that was meant to be everybody's favourite. Boroimir was the character that everybody was meant to hate first but later feel compassion with because of his heroism. Etc, etc. Gimli is really the underdog and I prefer him for this reason.
If we're talking about LOTR in general and not the movies, probably Frodo or Samwise. On second thought, Samwise, because of what New Troll said.