The title was one of the topics of discussion on our office forum. I wrote an answer there, but the character limit got exceeded. :D Not wanting to trim down the answer, I decided to write a post out of it and leave the link in the comment section. Here's my answer to this seemingly difficult question.
In short, as much as I like the Caped Crusader, I have to go with the Man of Steel.
Batman is one of the most epic characters created in the comics. The reason why we all love him is because he is one of us. A normal human with no superpowers. Yet he commands the respect of the entire Justice League. Hell, they even fear him sometimes. He showed us what any human can achieve with proper training and willpower. He is not an epitome of goodness. He has shades of grey. And we love shades of grey, 50 or otherwise. ;-) Although not monetary, he too faced hardships as a child. He has flaws and at times he fails. Making him much more human. And like they say, Batman is a symbol, anybody can be Batman. He fights his own inner battles along with the external ones. It is easier for us to connect with Batman.
But having said all this, my heart goes to Superman. Batman lost his parents? Sorry, but Superman lost his entire planet along with his parents. Yeah, he was too young to even realize that, but that doesn’t make it any less tragic. Batman was raised by a butler? Superman was raised by alien parents in an alien world. Batman became Batman primarily because he wanted to avenge his parents’ death. Superman was always Superman, and he decided to show the world how good one can be. Imagine being the most powerful person in the world, capable of superspeed, supersonic flight, superhuman agility, X-ray vision, heat vision, super breath, super hearing and the ability to absorb Sun’s energy. Now imagine being humble, not wanting to hurt or kill anyone, not going around boasting about your powers, not wanting to rule the entire world, not wanting to make a shitload of money and just going around helping people and saving the planet, daily and coming back to work at ‘Daily Planet’(couldn’t help with that wordplay :P). Hard to imagine, isn’t it? And he does all this to an alien species who call him alien even after all that he does. Because he empathizes with the human race. He knows what can be achieved with peace and unity. While Batman is trying hard to save Gotham from going to ruins, Superman is trying to take Metropolis into the bright and prosperous future. He is the quintessential good guy and better than all of us in every aspect. And we don't like it when others are better than us.
And all the people who say Supes is dumb, you don’t understand his powers well. He is fast not just physically. He is pretty fast mentally too. He has an eidetic memory. He can read an entire book in a matter of seconds. But his physical strengths are so overwhelming that his mental abilities are hardly highlighted. Batman knows how to diffuse a bomb? Well, Superman would just hold it between his palms and let it explode or throw it into the space. Also, in the Justice League, Bats is the brains and Supes is the strength. So there is hardly any chance or need to show his mental prowess.
Now coming to who would win in a fight, it would most probably be Batman. If at all they decide to fight that is. Not because Batman is better than Superman. But Superman would let the Dark Knight win. Because Superman knows he can take it all. Blow after blow after blow. Even if weakened by Kryptonite, he knows he can gain back his strength with a short trip to the space. He was able to live inside the Sun for God’s sake. He is literally God-like. Also Superman is always holding back. Never letting himself fully go. That is one of the reasons why no one knows the limit of Superman’s power. He knows no one can take it when that fist comes down with all its might. Above all, he will let Batman win because he is a good person deep down and a true incorruptible being.
Adding a dialog from the movie Kill Bill 2 where Bill explains why Superman is special and what makes him, him. This is one of my favourite dialogs from any movie and gives one of the best perspectives about Superman.
“Now, a staple of the superhero mythology is there's the superhero and there's the alter ego. Batman is actually Bruce Wayne, Spider-Man is actually Peter Parker. When that character wakes up in the morning, he's Peter Parker. He has to put on a costume to become Spider-Man. And it is in that characteristic Superman stands alone. Superman didn't become Superman. Superman was born Superman. When Superman wakes up in the morning, he's Superman. His alter ego is Clark Kent. His outfit with the big red "S", that's the blanket he was wrapped in as a baby when the Kents found him. Those are his clothes. What Kent wears – the glasses, the business suit – that's the costume. That's the costume Superman wears to blend in with us. Clark Kent is how Superman views us. And what are the characteristics of Clark Kent? He's weak, he's unsure of himself, he's a coward. Clark Kent is Superman's critique on the whole human race.”
So who's you hero.??