I can’t choose just one, so in no particular order.
Angel, BTVS & Angel - Angel was this grumpy old soul who made mistakes, who lost a son, and love, and battled his inner demons, and outer demons, and tried and most of the time failed to make the world a little better, not for glory, not because he was chosen, but because he decided to fight, and in the process he became a hero.
Jesse Pinkman, Breaking Bad - Take a stereotypical stoner drug dealer and make him pathetic, and vulnerable, and heartbreaking, and funny. Watch this malevolent force come into his life and manipulate him emotionally over and over, because this kid, who has no one is so desperate for approval, and love and acceptance that he suffers and suffers. The only thing I prayed for in this series finale is that Jesse would somehow survive and be at peace.
Chuck Bartowski, Chuck - he started as this goofball nerd and by the end of the series you completely bought him as this action hero spy stud. But, through it all he kept his heart of gold.
Matt Saracen, Friday Night Lights - He was thrust into the limelight by circumstance, but he rose to the challenge. He was the ultimate good guy, he took care of everyone around him like his grandmother. He was abandoned by both of his parents, but found a surrogate father in Coach Taylor. A lot of the heart of the show was bound up in this kid’s journey.
Ned the Piemaker, Pushing Daisies - Ned brings people back to life, but when he revived Chuck, the first love from his childhood, he was the one who gained a life. And even though he can never touch her again, their chaste love story is one of the most romantic I’ve seen.
Pacey Witter, Dawson’s Creek - If Dawson was the intellect, then Pacey was the heart of the show. He came from a blue collar background, he never expected to make anything of his life, he struggled after high school to figure out what he wanted to do with his life, he made bad choices, and he made great choices. He was wise beyond his years and he always (okay most of the time) remembered what was really important in life. He loved with all his heart and in this teen drama, his portrayal in the Joey love story was surprisingly mature. I hoped and wanted her to choose him at the end, and was gratified that the show agreed.
Oliver Queen, Arrow (so I had to include this one right) - The thing I find interesting about Oliver Queen is that he has never felt like he deserved happiness. He ran away from it before he ended up on that Island. And those five years of mental, emotional, and physical abuse as he said stripped everything away. Since then, he’s slowly rebuilding and reshaping himself, finding and appreciating what and who he is and trying not to make the same mistakes. He’s a painfully slow learner, lol, but I find his journey compelling and inspiring.