If you already have a BArch, then you should really think about why you want the Master's and what you want it to offer your future career.  Do you want to get into teaching and/or research?  Then a research master's may be the best choice.  On the other hand there are many specialist master's courses like landscape, urban design, sustainability, etc.  In this way you can add a specialism to yourself as a professional, and perhaps stand out from the crowd.  Or, perhaps you want to spend time looking at some sort of specific architectural design issues that you want time (outside of work) to delve into specifically.

If your only consideration was future employment, I'd suggest adding a specialty to make you more diverse.  Unless as I say you want your future employment to be in academia in which case research might be better.