Hmm. At 5'1", I'm a little surprised you'd be on a 43cm frame. I'm 5'2", and was fit to 47 or 48cm frames, depending on brand. Your proportions could certainly be different than mine, but make sure you get fit for your bike. It won't matter how awesome a frame you buy if it's the wrong size.

I avoided Cannondale and Fuji because the top tubes were too long for me. They don't seem to cater as well to short riders.

In the range that it sounds like you're looking at (aluminum frames) I did really well with Scott (Contessa Speedster), Trek (Lexa), and Specialized (Dolce). If you're willing to spend just a bit more, the Specialized Dolce Comp has carbon seat stays that I thought made a big difference. None of the other brands that I looked at offered that as sort of a compromise point between aluminum and carbon frames.

In the end, I was seduced by the carbon frame, and bought a 48cm Specialized Ruby Comp. It just came home last night. Can't wait. It was like a dream to test ride. The geometry was the same as the Dolce.