As far as formulas go, both are not perfect. For Audrey is thicker and only needs 2 coats, the first goes on pretty uneven. Turquoise and Caicos is kind of sheer, needing 3 somewhat thick coats for it to be opaque. I found Turquoise to be a little easier to work with.
Here is Turquoise alone (please excuse the the bumps on my index finger, I had some stubborn glitter stuck to my nail!):
And a bunch of comparison shots:
These shots emphasize the difference in color. In low light they seem almost identical. You probably don't need both. So do I get rid of one? Of course not. A girl needs back up bottles of these things!