'Pretty Little Liars' Star Lucy Hale vs. Pretty Hot R&B Star -- BIKINI OFF!!!

Two hot women ... two tiny bikinis ... but you can only CHOOSE ONE!!

First, "Pretty Little Liars" star Lucy Hale -- she's 24, she's in Hawaii, and she's smokin' hot.

Choose wisely.

Bonus Fun Fact -- besides being a huge singer, Milian also co-wrote the Justin Bieber smash hit "Baby." So, take that into consideration.