IBM had its problems with production, but overall they are fine. Since the military had strict requirements of parts interchangeability and steel hardness/heat treating, one is about as good as another. I lean towards Inland as the "best", since they developed most of the gauges and drawings for the initial production, much to Winchesters chagrin. They were VERY good at assembly line production being part of GM, and it showed. They also had some very good people working for them, and they helped out most of the other manufacturers.
Once they were built and accepted however, they were pretty much the same. Now, the name is the selling point, and IBM, Rock-Ola and Winchesters command premiums, even though there is nothing special about them. Once you go beyond the names, then the more rare receivers/subcontractors and variations become desirable. What's the going rate up there for good USGI Carbines?