The style Ali had the most trouble with were smaller, quicker men and of course men with good left hooks. He had problems with Frazier who was the perfect style to give him trouble, as you mention, Chuvalo did better than a lot of people remember against Ali in both fights. Norton gave him problems because he was quick and he had a strange style so he's a little bit of an anomaly. Spinks was in the mold of guys who would give Ali problems and he caught Ali when he couldn't put up much of a fight. Lots of guys had good rounds and good moments against ali, patterson, foster, lyle. One thing about Ali is that he didn't take the sport as seriously as he should have, I think it worked both ways, when high pressure fights like frazier or foreman came along, he wasn't even close to being overwhelmed by the moment but on the other hand, him goofing off got him caught by Cooper and lost him a lot of rounds later in his career. Joe had one thing over just about any other great fighter, he was known to stay on top of his training, give or take a rumor or two, he was generally one of the most consistent champions ever, the 11 mos and change holding the title is no accident.
Joe maximized what he had more than Ali did I think. I still think ali makes it an easy decision win in his 60's prime. Joe wasn't the frazier, chuvalo type. And Ali also had layers to go through to even get him into trouble, first, in the sixties it was his marvelous movement and defense, in the seventies it was his inhuman toughness and total refusal to be kayoed. Frazier should have kayoed him in the first fight, hurt him many times, knocked him down once and had him wobbling like a drunk in the eleventh. Alis' reaction to the 15th round knockdown? He gets up at 3 and goes on to win the rest of the round, even taking a couple more vicious shots, the dude was special.