The difference is really that BJJ focuses on the ground while JJJ focuses on stood up techniques and self-defense. There are rarely competitions in traditional Dojos, but in BJJ, they are likely to be commonplace. In terms of which will be more fun or more effective; again it depends on what you put into it. Any martial art can be useful or useless, depending on how you train and how you listen, to the instruction. Whatever it is you choose to train in – pay attention and train hard. The rewards will be intrinsic.