Short answer: BJJ is better than Judo for MMA. However, Judo is better in a street fight.
Long answer: First of all, I practice BJJ exclusively, so even though I'm just a white belt, I'm not biased towards Judo.
BJJ probably has a better ground game than Judo and a real fight usually ends up on the ground. Since going to the ground on an octagon's canvas doesn't usually end the fight, this is where BJJ shines. BJJ usually includes a very big part of fighting without a gi, while Judo completely neglects this aspect. Present day MMA is mostly fought without a gi, which gives BJJ a huge advantage. Fighting without a gi greatly reduces the capacity to grip your opponent. However, all of this changes in a street fight. The gi simulates regular clothes and people in the street usually wear clothes, so you get a formidable grip and slamming an opponent head-first on concrete will usually send him into a coma, so it will take less than 3 seconds to take an opponent out of the fight, 100% of the time. Not only is this extremely effective against one opponent, but also much more so than BJJ against several opponents, for obvious reasons. Whereas with BJJ you take much longer to dominate an opponent and you have to take him to the ground first, and takedowns are much weaker than with Judo, so it's high risk and much lower percentage. If you only practice BJJ, many times you will have to pull guard, which is very dangerous as the opponent can escape and ground and pound you if he's much stronger than you. It also leaves you open to his friends stomping and soccer-kicking your head into another part of the universe. Even when you get top-control you're extremely vulnerable to this. With Judo this will never happen. Also, Judo has a very strong ground game too, at least with clothes or gi. From all the videos I've seen of Judo vs BJJ with BJJ rules and gi, Judo wins far more often than not. Therefore, BJJ is better than Judo for MMA, and Judo is better than BJJ for street fights and self defense. But again, this is just a BJJ white belt's humble opinion.