I recommend A Beautiful Evil. 
 ***** 
 Darkness Becomes Her is better than A Beautiful Evil but this second book has its own merits. Athena is menacing as ever, and for that, this book is quite the bomb. 
 Ari is still bad-*ss but there's this instance that i found her incredulous. idiotic, even. Sigh. i would like my heroine to be confident and skilled in battle, but i do not want her going into one without proper arsenal. Ari, you're fighting a goddess (Athena, no less!), for goodness sake. The least you can do is make the capturing a little difficult. i find it rather insulting to have Athena slaughter you at her silver plate because of your stupidity. 
 Sebastian is almost a god in this sequel. I am so envious of his powers! Man, now you look positively hot. *Ahem* 
 The unusual portrayal of Pandora's box is alluring. The agenda behind Athena's relentless pursuit of Ari's power is shockingly... human. I loved that. 
 If you dig the first book, you will dig A Beautiful Evil even more. Powerful Athena versus an equally powerful god-killer. =) Hoho! Cat fight has never been this delicious to read.