My two cents...
I've got a Cannondale R800 Feminine, which is several years old and fits perfectly. I'm 5'4'' and it's a 50 cm frame.
This year I wanted to go faster, and bought a Cannondale Six13. It's not women's specific, so I went to a 48cm frame, which has a shorter top tube, and swapped the handlebars from a 40cm to a 38cm, and also got a shorter stem.
I spent a long time with my bike shop getting the fit right. My advice would be to go with the best shop. Many of the bikes these days are similar, so it comes down to who you trust, who's the most knowledgable, and who offers the best customer service.
And don't be afraid of aluminum. If that's what you can afford, there are plenty of bikes out there with a good ride.