I really like both bikes, and still hoping to get a MERC with 7 speed (brompton copy). I have a birdy, and chose to get that first for versatility.

This is a personal preference decision really. Consider how you are going to use this bike, prioritize functionality, test both, and decide then. For city use, Brompton is a good choice, but I don't know about touring on it. For longer distances and speed rides, the birdy will take it over brompton. They both cost a pretty penny so make sure you make the right decision.