Howdy
USFA is an American maker based in Hartford Connecticut, not too far from Colt. USFA is the only American maker of a replica of the Colt Single Action Army. They use very high quality steel and give the parts inside the gun a very good going over before final assembly, to make sure everything works just right and the action is smooth. USFA does a better job than the Italian replica makers in this aspect, most Italian replicas are slapped together with very little attention to detail down inside the gun, and the parts often need some smoothing out to get the guns up to optimal performance. The difference you are paying for with USFA over Italian imports is for the extra effort that goes into the guns, and American wages. It is often debated, but the quality of USFA revolvers is probably every bit as good as Colt's. The main difference is because of the Colt name, their products will appreciate in value over time, USFA will not. Any revolver patterned after the original Colt SAA will perform fine, but it must be remembered that the design is over 130 years old. They were never intended to be shot as much as we tend to shoot them in CAS, and they can sometimes suffer from mechanical problems, chiefly broken springs.
Ruger single action revolvers on the other hand were completely redesigned from the ground up back in the 1950s. All the leaf type springs were changed over to coil springs, which are practically indestructable. In the mid 1970s Ruger single action revolvers were again redesigned, this time making them completely safe to carry fully loaded with 6 rounds in them. Although a modern Ruger single action revolver looks reasonably similar to the old Colt SAA, the interior lockwork bears little resemblance to the old SAA. This is part of the reason for their strength and reliability. In 2005 Ruger introduced the New Vaquero, scaling the gun down to the same size as the Colt SAA. They are no longer capable of firing the massive loads that the 'original model' Vaueros were, but they are still just as reliable and will shoot just as long without breaking down as the earlier models were.
You pays your money, you takes your choice.