what i've noticed (at least for the idols, not rnb)
Jpop - They tend to pick girls with potential & debut them asap without perfecting their talents b4 debut. i think jpop fans like to watch their idols grow & improve
Kpop - They tend to debut extremely trained idols, if you're not able to sing live or dance, your debut won't be noticed lol. and the trainees seem to go through more intense training than jpop
i love both tho~ and it honestly depends on what people listen to in kpop, it's just the more popular songs that are "european/american". like, take IU for an example. or girl's day, orange caramel, apink, and even other groups, if you listen to their albums, you'll hear a great variety of songs. and if you listen to other korean music like tasha, tiger jk, baby soul, leessang, BoM, etc, their music is just really amazing.
and for jpop, it's like an entirely different thing from kpop. so, i really won't be able to chose one over the other because they're both so different. i do love watching the idols grow, and improve their dancing/singing, and the songs + dances are a loot cuter (and easier to follow LOL). although, i prefer kpop ballads over jpop ballads (idol-wise anyways). because kpop ballads feel a lot more smooth than jpop ones (less bobby, idk how to explain). for rnb, i love it as much as korean ones, there's amazing singers too like MAY'S, thelma aoyama, may j
i have yet to find a girl who raps as well & powerful as tasha tho
so my conclusion: both can't really be compared, but i'm able to enjoy both because they're so diff
it just depends on my mood and what i want to listen to~