I believe that if Tyrion was born a "whole man" then he would not have the noble heart. Sure, that heart might be there at all times, but it would not have had a chance to shine through being a proud member of House Lannister. He had to suffer through the hardships of being a dwarf son to arrogant Lord Tywin in order to have that heart. The same thing with Jaime... He had to suffer defeat in battle, ghastly imprisonment at Riverrun, a harrowing journey through central Westeros, and the maiming before his noble heart shown through. And then at last he is relieved to see his family again and they shun him! Before all that, Jaime was a murderous soldier of the Lannister House, and was quite content at being that as long as he can have his sister. Tyrion is not the most honorable either, even after all. He killed Shae and Tywin, his lover and his father, despite their turning their backs on him, they were his family more or less. And he was very sneaky about it. Don't get me wrong, Tyrion is also one of my favorites and I understand and sympathize with why he did that, but he did that for bitter vengeance and to promote chaos in the kingdom. I don't think Tyrion is all that good-natured. I think he is good-natured when he needs to be, but I also think he is not as evil and conniving as others. He is certainly no tr****r, and I see treason as being the ultimate evil in ASOIAF.