how did Rob Hall and Scott Fischer differ in terms of character?

Both men are generous and ambitious. Ron Hall was definitely the more consciencious and cautious of the two. 

Hall was in general an easygoing guy, but his nice-guy personality masked an intense desire to succeed—which to him was defined in the fairly simple terms of getting as many clients as possible safely to the summit. He also paid careful attention to the details: the health of the Sherpas, the efficiency of the solar-powered electrical system, the sharpness of his clients' crampons. He loved being a guide, and it pained him that some celebrated climbers didn't give his profession the respect he felt it deserved.

Fischer took more chances, as he was determined to make his place among the commercial climbers.