Having done both Judo and BJJ, as to the efficacy, or of the "style" in general, without any cross-training in anything else... which hardly ever happens in any decent school, dojo or program, personally I'd take Judo for one reason only. In the BJJ schools I trained in/at, the vast majority of the training time was spent on the groundwork elements of BJJ, which to me acted to exclude "how you got down there."
I'll grant you, two folks with similar athletic skills and training mindsets... one goes into Judo the other into BJJ. Average progression, and I'd have to take the BJJ person on the ground every time, if that's what the conflict is. But, if they start in any other configuration other than both kneeling, or back-to-back, or wrestling style start of session, I'd go with the Judo.
I know other BJJ schools have more emphasis on their stand-up to ground portion, which to me would be key for it's use as a SD option, I've just never trained at one, or even visited one, where the emphasis was on the well-rounded, rather than BJJ tournament, game. Note, nobody in these two schools did any MMA type stuff at all. It's a very small sample size, and I get it.