A top reason that Tormach is better is the lack of a quill with the Tormach. The lack of a quill means higher rigidity and better surface finish. I have been using a similar size (to the Tormach) manual Rockwell vertical mill
http://www.lathes.co.uk/rockwellmillers/ for the last 8 years. The Rockwell has a quill. There is an improvement in surface finish with the Tormach without the quill. The quill spines have some backlash that adds to poor surface finish especially at higher spindle speeds. The Tormach is more rigid than the Rockwell. Also with the CNC Tormach there is no need for hand wheels. Since buying the Tormach the Rockwell has been not even been used. The Tormach was designed from the beginning as a CNC mill. The X3 is a manual mill that can be converted to CNC. The point is that features necessary for manual mill operation, such as the quill, are harmful to the performance of a CNC mill, sacrificing rigidity and surface finish in the process.
Don Clement
Running Springs, California