Standing, the judo guy should have the advantage of being able to take the bjj guy to the mat at will. It depends from there. If the bjj guy remains relatively unscathed it comes down to what position he landed in. Judo guys smother and stay tight, and the subs come fast. They keep base really well. Guard gets problematic, and comes down to whether the judo guy treats groundwork as an opportunity or a nuisance. If judo guy gets swept or gets his back taken, its probably over. Bjj guy is patient, methodical, and sure as hell doesn't want to stand back up.
Its fair to assume judo guy throws better and bjj guy is more crafty on the ground, so it's the transition between those two where the magic happens, and what makes or breaks it for either guy.
But it really comes down to the player. A lot of bjj guys cross train and have top heavy games, and a lot of judo guys have vicious ground games. There's also the leg lock factor, which judo guy won't know shit about unless he cross trains.
Bjj rage will tell you bjj wins because it's the coolest, because he like totally tapped a two stripe white belt who said he was a judo black belt one time.
Some of the judo guys will be too proud to admit the bjj guy has a better shot on the groun, then something about how it depends of the match is on concrete or igneous rock or aids needles or what's ever.
The wrestlers will be butthurt they aren't included in the conversation, and tell you you're a pussy and dont do enough conditioning and that they're hungry.
Oleg ratkawhatever will be in here to tell you sambo is the best, and even though you can count the number of american sambo gyms on one hand, you should train sambo because he trains sambo and that's pretty much all he ever posts
then the next ten or so pages are gonna be some version of 'nuhuh' and 'yuhuh' and bullshit irrelevant highlight videos and a few white/orange belts repeating almost verbatim everything weve already said ad nauseum, a few people will reply with such flagrant disregard for english youll simultaneously wonder how they manage to run a computer and lose all faith in western education, Richard will post something real creepy, someone shills some upcoming seminar or fucking DVD and then I'll be an ass and post a meme or esoteric pop culture reference because im am ass and then one of the 10th planet guys will say blah blah rubber guard and then we'll hear even more anecdotes about one time during practice from some random ass three stripe white belts.
And then finally everyone will agree that both dudes should have just cross trained in each art and that's always the best way. Except Oleg, who will still insist sambo is superior because mother Russia.
And its all the same fucking thing.