For occasional suspension work, I would buy a Campbell-Hausfeld such as this one:
http://www.chpower.com/webapp/wcs/stores/servlet/chPrd3_10051_10001_97793_-1_10676_10708_
I have one for weld chipping, suspension work, and masonry work. It's a fine little tool for $25.
The only place were I would spend a lot of money on an air hammer is if you're bucking rivets. In which case, a $750 Chicago Pneumatic or Cleco is money well-spent.
Tip: The longer the air hammer's barrel, the fewer hits per minute, but the heaver each blow is. In aviation, we denote the size of the gun as 1x, 2x, and 4x Though, guns up to 10x or so are available. I'm sure there's a precise standard for air hammer sizing, but I've always gone by this rule of thumb.
1x guns are stubby, with about 3,000 or more hits per minute
2x guns are about 6" in length, with about 2,500 hits per minute
4x guns are 8" or so long, with about 1,500 or fewer hits per minute.
For suspension work, I'd want a 2x or 4x gun.