I have a Hutchins air file. Excellent tool. Bought 30 yrs ago, and still works like new.
Dynabrade makes good stuff no doubt, but some of their prices are sorta tough to swallow. Never have priced their D/A so I dunno how it compares to other quality ones.
I've also got a National Detroit D/A and would buy another in a heartbeat. http://www.nationaldetroit.com/global/ Still US made. They are the original inventor of the D/A sander and were the only producer of a high quality one for a number of years.
Also have a couple 20 yr old Aro palm orbitals that are very good sanders. I think Aro got swallowed up by I-R though, so they're probably made in Upper Slobovostan these days from melted orange juice cans
Added: all the above tools use a surprisingly small quantity of air as compared to any of the 3rd world copies I've had. Over time they pay for themselves in saved energy costs, and the pleasure of using a good tool sorta comes along free in the mix. Other than my dad, NO ONE uses my sanders. A ham-fisted jackass whose grip is calibrated toward snagging parting lines off castings will ruin the pad on any of them in a matter of minutes. Good pads are expensive, and the cheap ones are absolutely useless. I'd rather use a Harbor Freight D/A with a 3M pad than my N-D with a $3 chinese pad installed.
Can't comment on the others, but I used two different 6" National-Detroit Model DA sanders (this: http://www.sjdiscounttools.com/nddaq6.html) at work for 10-30 hours a week for two years. Never had a problem with either of them, and they are pretty comfortable to use. They are reasonably quiet when run under anything but no load, too. If I ever buy a DA sander of my own, it will be a N-D.
I need a DA sander for my car. I don't have much idea about it. I have searched on the internet to get the best one. I went through inspiringhomestyle.com , they have reviewed few sander. I decide to take PORTER-CABLE 7346SP for my work. Is it full fill my purpose?