The main difference is the lack of confidence on the part of the dwarves. They have witnessed Smaug's power and are terrified of him, despite the assumption that he is sleeping as he hasn't emerged from the mountain in a long time.
Bilbo has a great deal of confidence, which in some way may simply be a reflection of his hobbitness in that hobbits are often stubborn and in some ways this leads them to a form of bravery or overconfidence. Bilbo also has the advantage of the ring up his sleeve which he knows will allow him to disappear when necessary.
Bilbo is also immensely curious and for him the journey into the bowels of the mountain to see the treasure is exciting as he has only heard stories of their great treasure and the majesty of their halls.