First one, the Frivole!!
The Cosmos is gorgeous but I'd think you'd be limited in your choice of clothing. The all-diamond is neutral and you could wear whatever colour you like!
And also IMHO (mine only, of course), the Cosmos is more grown-up whereas the Frivole is more "girly" (and therein lies my own "dilemma" also, lol). So, it'd depend on your age I'd think; or maybe I'm wrong (I reeeally hope I'm wrong about this, lol).