Most of the items the vendors carry are all the same; repro stuff made in the far east. And it is usually not of the highest quality.
So the only thing to look at in most cases is price and service. I find that Truck Shop (in California) has the lowest prices for most of their inventory. Usually not much lower than Chevy Duty, and if you factor in Chevy Duty's free shipping for a large order, you might come out even.
But Truck Shop's service definitely leaves a lot to be desired. I usually go with Chevy Duty, I have never had any complaint on their service. Or at least, none that they did not quickly resolve.
But some vendors carry stuff the others don't. I buy from Chevs of the 40s occasionally because of that. But they are probably the most expensive. I suggest you get catalogs from as many as you can.
Check the "links" section of this fine site to find the vendors mentioned.
