Obito back in the day was awesome, what with the whole Rin dying and his combat style and all, all of the emotion involved with his character is just amazing.
Madara on the other hand is a legend, and legends tend to get fans excited.
I would say that Obito beats Madara out by a hair but Madara is still very very cool
Madara is definitely "cooler" in a sense of calm an confident. Obito trying to destroy the world because of a girl is really cliche and lame. I loved the way he fought in 605 though.
Madara is strong, he's a beast and he can fodderize just about anyone but that doesn't make him cool. His motives are selfish and hate based.
Obito on the other hand; his motives are based on something he wants more then the world itself. He just wants a world with Rin and Kakashi where Kakashi didn't just break their promise, but killed her himself. His motives are fueled on love. He will do ANYTHING to the world he inhabits currently to make this happen, and I think that's pretty cool.