As stated above, you should go with a DA polisher (random orbital) rather than a circular rotary device. The DA polisher might not remove defects as fast or have as much correction capabilities, but they are the most user freindly when it comes to not burning through your clear coat while correcting the paint and will still net you great results.
Some known good brands would be Porter Cable, Flex, Rupes, and Griots. The main differences are the power levels and the "throw" of the machine. Most DA polishers have a throw of 4-8mm, but some models have a throw of 15-21mm. Having a bigger throw allows you to better correct larger surface areas at a time.
Since DA polishers are limited in their power, I would recommend getting the 5" back plate over the 6". The 5" plate will allow you to use the 5.5" pads which is about as big as I would go. The limited power and rotational design of a DA polisher causes the machine to stall while using the larger 6.5" pads.
I purchased a Porter Cable 7424XP with the 5" back plate and was thrilled with the results that I got. If I get some extra cash, I'll probably invest in a smaller back plate and pads in order to get the areas that the 5.5" pad won't fit (I have to do these spots by hand). There are better machines, but this particular one is hard to beat for the price. I usually just remove the side handle while using the machine. If you do get a Porter Cable, make sure you get the XP model (it's the newer upgraded version).
Which ever brand you decide, make sure you get the right size back plate and the proper pads for each product you use. I purchased mine as a kit from Autogeek that came wth the hook & loop back plate,a variety of Lake Country pads, a pad cleaning brush and a few other things.
If you have time, search around on the Autogeek website or even on their forum for useful tips when it comes to brands, pad types, and proper techniques. Mike Phillips is one of the best in the game and has tons of useful "how to" videos and threads on all these things.
Heres a couple links to give you some perspective. :thumbsup:
http://www.autogeekonline.net/forum...se-right-polisher-your-detailing-project.html
http://www.autogeekonline.net/forum...her-rupes-griot-s-porter-cable-meguiar-s.html