how about UV/AoHu for more variety in the Diamonds? should still be pretty insane yet possible.
Arena Master on UV/AoHu would be the easiest diamond by a long shot. WINNING UV/AoHu would be the easiest diamond. It's just not possible to make a badge that's diamond-hard without it being on Nightmare! difficulty.
(Except for UV with fists, because that's just ridiculous and is probably the HARDEST diamond.)
EDIT: Oh hey, there's also UV/AoRA/100%. UV/AoHu/90%+ would be diamond-difficulty, then.
I'm not sure about AoSh, though. AoSh is the easiest challenge for everything but beating the Arena Master, so I guess I can see where you're coming from.