IDK Diamond is still young, someone will likely scout her from this. Sure she has a great voice, but I personally don't find her likable at all.
Arin is the full package and has way for star appeal. That's what separates X Factor from the rest, it looks for stars, not the best singer. Although Lord, the public seems to remain ignorant of that fact given the voting. The market is saturated with banshees, even well known one's like Maria and Xtina are flopping. Too many great voices with no appeal have one these shows only to flop when it came down to it.