about lvl 21 u wont get much exp anymore. I recommend it to do it until lvl 52 or 53 idk. But if ur a healer or a Poko then go ud3 hard. The exp is so insane. U can do it until lvl 58 or 59 like that. and if u really do it like dat. u can save tons of Papaya quests in the end for lvl 80 update

for those who going to do ud3 I tell u the exp. from lvl 45. 1 mob gives u so about hm 1k exp. AFter exery single round u should have earned mmmmm 13k exp I guess. at lvl 54 ud3 hard u earn almost 30k