USFA simply builds a better SAA than Colt does and they do so for less money. Period. Sure, Colt true-believers will defend them to the end but when you compare the guns side by side, inside and out, it should be clear to anyone with a critical eye who is building the better gun. A great many 3rd generation Colt SAA's are way over polished. You will see rounded off edges, dished out screw holes, wallowed out lettering, etc.. You won't find this on a USFA. They always appear to have been hand polished. The flats are flat, the edges are crisp and even, the lettering sharp, everything is simply done better. USFA also gets their dimensions right. No huge chamber mouths, yes I have .457" mouths on my New Frontier. As well as all the other aforementioned maladies.
On the inside, Colt's greatly benefit from an action job. They are typically as rough inside as an Italian replica, though my NF was worse than late model Uberti's. USFA's are as finely machined and well finished on the inside as the outside. They need only a spring swap.
USFA offers way more options and chamberings than Colt.
A USFA standard single action is comparable to a Colt in finish level but costs $200 less.
USFA offers a true 1st generation replica in the Pre-War model. It has authentic finishes that Colt has not used since WWII and costs the same as a standard white-sided hammer, hot salt blue Colt.
The resale/investment rhetoric is just that, nonsense. Folks repeating what they've always heard. Colt SAA's have been $1200 for as long as I can remember so your brand new 3rd generation will never appreciate in your lifetime. Fired or unfired, there is nothing magical about a 3rd generation Colt's value. A NIB 3rd generation Colt from 20yrs ago is not worth any more than a brand new production model, except that the new gun will be better. If you want an investment, buy a 1st or 2nd generation Colt.
If you want a 2nd rate reproduction with the famous name, buy an older 3rd generation Colt.
If you want a good SAA that still costs too much but has the famous name, buy a new Colt.
If you want the finest SAA money can buy and the best value, get a USFA.