^ Well Dongho and Eli have straight up bad Japanese, but the rest have pretty typical Korean accented Japanese. The main problem is slurring words and the way they pronounce t and d.
I do think Soohyun and Kiseop (and AJ? I don't know, I haven't heard him enough) have the best grasp of how Japanese is supposed to sound.
I expected Kevin's Japanese to be worse considering his "boku no yume wa sashimi" thing from a long time ago, though that had nothing to do with pronunciation, lol.
EDIT: omg loling @ the Tick Tack lyrics someone posted. Clearly transcribed by someone who really doesn't know Japanese at all and just can't hear in general because the English is all wrong, too. It's actually a pretty big pet peeve of mine when people do this. If you don't know Japanese, your lyrics are going to be totally wrong and you're in no position to write the lyrics by ear and post them on sites as if they're the real thing. Anyways my favorite part is "zankoku na kame ga atte." Who knew this song was about cruel turtles?
Actually the first four lines are almost exactly right except it's "kasanete" not "kasanette."
They could have helped their cause by looking these words up and making sure they were real words and not just gibberish.