Isn't really an apples with apples comparison. Aperture is very different, as the Vixen (being a bigger light bucket) will collect 2.48x more photons than the NG per sub. This will impact on your SNR and affect the finished image even if workflow is the same.
As Brent pointed out, stars look bloated in the refractor image. Do you have a field flattener for the NG? Or perhaps it was just that your focus was off.
The
VC200L is actually specced at f9, so I assume you're using some sort of focal reducer to get f6.4? Either way, focal lengths of the two scopes are also different, and this affects both image scale and guiding performance. Assuming you used your 5DII, the image scale is 1.03 arcsecs per pixel for the Vixen, and 1.93 arcsecs per pixel for the refractor.
Keeping all those things in mind, another image and equipment comparison when all the bugs have been ironed out of both systems would quite interesting.
Equipment issues aside, I much prefer the image from the vixen. Tighter stars, not as black clipped as the refractor image, and to my eyes a more 'natural' colour balance.