If you're a fan of her old music, I'd say go with "LOVEppears". It's got some nice tunes on it.
"Duty" seems like a good album. Go with that if you really like Ayu. I think that's an album that'll be worth buying.
"I am.." is (IMO) Ayu's album. Because she composed practically all the songs on there!
And last but not least, "Memorial address" has a lot of powerful songs. Maybe ''powerful'' isn't exactly the right word --
-- but they are so amazing to me!