From Tattoos I've got on myself, machines I had chance to see and feel and feedback received from tattoo artists I formed my own opinion on this topic.
Rotaries and Coil machines differ in skills needed by artist. Coil machines and their variability in settings require less mastery from artist in terms of using properly set machine, but require more skill at setting one properly to make whole experience (and healing) more of a pleasure than torture. That reflects on work quality as well. Rotaries on the other hand require more skill, feel and control from artist. This by no means put artists that use any of these lower that the others. It's just that some people have more skill at controlling their hand and can get away with less precisely setup equipment while others are able to setup their equipment with jewelers precision to work more delicately on skin, placement specifics etc.
And because of that we will always see perfect and terrible tattoos done by either machine. All in all it all nails down to master to select equipment that suits him well. Just like in music- a good percussionist would probably hurt your ears badly while playing a guitar.
