I've thought over your question and I'm kind of looking at the literary figures more than the others. Yet it is hard to hone in on just one.
If Harry Potter is such a popular character amongst young people in this mad mad world, I'm actually quite happy that someone who uses his wits and his heart is the hero of children everywhere. How lucky we are that someone like Harry and his friends are adopted as heros.
What I admire most about Harry is that no matter what, he remains himself, despite temptations he is emminently human.
If you really want to go for a popular heroine though, I've always thought Lara Croft is quite revolutionary as though she's a strong heroine, crafty and physically quite strong, she's really feminine..um er...and if young boys manage to play the game using a female character who outwits men, then the archetypical hero has evolved somewhat!
When you raise a girl, you notice the paucity of female characters who are strong role models. I used to hate the Cinderella and Snow White and that lot, yet in the long run, my daughter is a very strong character and no wimp. But a girl can always admire a male character as well.
A boy on the other hand rarely admires a female character for her strength whether it be mental or physical. Or he won't admit it! Lara Croft seems like the first one who's appealed to boys as well as girls.
If you've never played the Tomb Raider game, check it out!
As to literary characters, Bridget Jones is extremely popular.