TL;DR entire thread.

If you can't be personally fitted for a frame/bike at your LBS, here are two things to use as a guide for a road bike frame:
stand-over height. should have a minimum of 1" between groin and top tube. Preferred is 2-4"
Top-tube length, should be: (your inseam x 0.67)

that's a good starting point.
Using that, I take a 48-50cm frame on most road bikes, or a "Small"
I'm 5'7" with 30" inseam.