IPTV66 STB or Coach Potato?

IPTV66 Help here!
Personally

If your running emulator your running 3rd party program anyways go with couch potato

keeps everything within Kodi

IMO picture quality will be the same since your using a 3rd party program to access the service anyways why not have it set up as an all in one solution
 
I suggest reading up on the different options for getting IPTV, vs. asking for direct comparisons. An STB, the STB EMU and a Kodi Add-on are completely different approaches, and ultimately it comes down to preference and utility, rather than performance.