Most lowers are machined from drop forged platters. A very few mill from "billet," which is basically a hunk of aluminum. I don't know of anyone casting lowers at all in this market, other than FRN polymers.
There are a few forgers, who machine. There are a dozen or more machiners, who buy platters and finish to their specs - including Colt. Most of the roll marks on the market, and there are over 5 dozen, all come from the same handful of machiners. That makes the lower market largely a commodity item, mass produced all very similar specs, and literally interchangeable. Most parts will install equally well in any of them, and they all shoot the same.
As said, pick a roll mark for what you want it to be. I bought an AGP, because I caught it on an introductory sale for $79. There are others on the market for less. I like what I got as AGP is a turbo parts kit maker in the automotive aftermarket. They know machining to spec, as a turbo spinning at 120,000 RPM doesn't tolerate sloppy work. My lower has all the platter flash removed, a great finish, and even an adjustable trigger travel screw already installed, which took 80% of the creep out and made it that much better. Their logo isn't a huge cartoon, and the markings are CNC made, not a metal stamping smashed into the surface.
If you are shopping for a lower, consider the total cost to the FFL and his fees, which are mandatory. It may be just as cheap to buy his off the shelf, given it's something you like. Even more so, complete lowers with all the parts are priced about the same as a bunch of parts or kits mailed separately. If you need to save money, buying an assembled lower and separate upper can be very competitive - if they have the features you want.