You need to look for hull thickness and rib placement.
I would not buy an alum. boat with ribs any farther than 12" apart.

not sure what all you plan to use your boat for but I would give a good look at MarshRunner boats, they would be quiter and I think price wise they are competitive of aluminum along with now weld to break

Those are some nice boats

Take a look at the new Edge boats Lake Area has now. Like nothing sold here before. I have a 556, 15'2" long, 56" wide, longitudinal ribs, hard to describe the bottom design, a stepped V bottom with reverse chines on the outside edges. From the transom to where the rake starts, the boat is 8 degree V, from the rake to the front it is 12 degree V, a very well built, dry ride, super faast hull. I run a 4 cylinder, 4 stroke, EFI merc with a 60 ecm, boat runs 52 mph wi5th me, fuel and battery, 49 with another man. Will turn on a dime. Boiat runs like a pad bottom boat.
http://i126.photobucket.com/albums/p...1/IMG_0327.jpg
http://i126.photobucket.com/albums/p...1/IMG_0326.jpg
http://i126.photobucket.com/albums/p...US1/good-1.jpg

Weldbuilt & Weldcraft are good boats for river and calm water. Don't hold up great in pounding rough water..