If you can get the EPA cat's then I would go with the magnaflow, the CARB cat's are not cheap.
if money is a issue there is a company in Canada that sells some very cheap EPA cat's but no idea how long they will last
the cheapest CARB cat's are catco they have not been lasting me very long but I am not your average driver, my foot is in it all the time.
Eastern makes some for the 5.3l that are comparable in price to the magnaflow but I have never used them since they don't make any for the 6.2l
the magnaflow can be very pricey for the CARB ones, they appear to have a price lock with anybody that sells them, some companys have that ability to influence the price.
no one is allowed to (publicly) sell them cheaper than the price set by the manufacturer, otherwise they get blacklisted and can no longer purchase them.
that's why when you see a price for something/anything online and it if say's "see price in cart" that is there workaround, once you have it in the cart then you can see whatever discount they may offer and the publicly displayed price still meets the guidelines required because any discount is hidden.
Technically a price lock (resale price maintenance) enforced like that is illegal, but nobody does anything about it.
The Federal law and State laws can conflict so doing anything about it takes money.......
kind of like weed being legal in some state's but still illegal at a federal level.