.The Williams has a (much) better fit and finish that's nicely polished and rounded where they should be rounded off. The P T & G is more "blocky" around the trigger finger guard. Lots of reports, to me anyway, about the PTG floor plate "popping" open during recoil too. Here is a Williams unit that I sent to Robar for a NP3 finish to match the 700 SS action and primarily protect it from rusting as I bought it blued in the classified's right here.
Not the greatest pic, but here is a Sunny Hill one piece unit that I had finished in Black-T.
Here's a sleeper that not many folks mention probably because McMillan has it hidden on their website. I can't mention who makes the unit for them, but lets just say it is as nicely finished as the Williams and Sunny Hill piece. It is made from machined aluminum and anodized black.