if your looking for something with a bit of bite to it it, you need a rotary , if your just after a quick shine up job get a DA, although ive had good results from flatting marks with a DA , its all down to the user who is using it . takes years of practise if you ask me, ive been polishing cars (i do bodywork for a job) for years and i still learn new tricks etc and teach people who have been doing it for alot longer different ways.