Marshall - 5:08 am on Feb 25, 2013 (gmt 0)
Personally, I am a proponent of separate sites, especially given the wide variety of devices on the market and varying screen resolutions. I abhor making a visitor download information that will not be displayed (responsive designs) versus giving them what exactly they need. That being said....
I recently adapted one of my sites to a responsive design and in testing it, found that my "mobile friendly version" did not necessarily appear well on some devices, specifically tablets with landscape widths of 1280px. No matter which way you go, responsive design or two sites, it will never be perfect and some portion will have to adapt. It truly is a no win situation.
However, if I must pick one way or another, I would stick with two sites as a) it is easier and b) none of my sites has suffered in SERPS using that method.