theres a couple things you gotta look at, JJ has been in the game just as long as dre, since the early 90's. he produced a candy man joint - knockin da boots. johnny j doesnt make beats with samples in them anymore so in originality i gotta give it to JJ. JJ is better to listen to for mellowing out or something
Dre has been one of the top people in the game as far as producing and his shit is REALLY hot, however he doesnt always make the beats now. he has his lil production team do them and he takes the credit, ask scott storch and whatever the hell his lil team is called. Dre has more club type beats
i think that these 2 cannot be compared because their style is completely opposite of each other. it would be like comparing east coast rap to west coast rap, 2 completely different styles.
oh and JJ sucks balls at rapping for the dude wanting to know...