I use my rotary as a first pass on every detail I do and 9 times out of 10 I will use it to finish,although I do use the rupes 15 to get real close to things,the trick with the rotary is the heat and how you control it, for example in the depths of winter when you have no heater in the work area,your best friend is your rotary to heat up the clear enough to get it to a working temp and keep it there,as for the best shine at the finish,i have used both and couldn`t call it,all I would say is that the rotary gets there a damm site quicker than the da,
and just as a side note every time rotary is mentioned here the word burn is used,well I have been using a rotary since 1985 and have yet to burn ANY paint,yes you have to take care but its like anything once you are used to it,having said all of that if I was doing cars that only have a few swirls and general dealer damage I would probably be more inclined to go the da route,but alas I don`t have that luxury as my bread and butter work is scratch removal on very tired cars,to each their own