[Leica] OT: Camera, viewfinder and/or film format best for manual focus

[scott at adrenaline.com (Scott McLoughlin)]

I know many folks on the list have shot extensively with many different
film formats and cameras, so I'm wondering....

What camera's VF/ground glass/focusing mechanism (in any format
up to 4x5) is generally best for critical manual focus?

I know my buddy who shoots 4x5 uses a loupe on the ground glass
to focus.  Is this "as good as it gets"?  Or will a waist level finder
with a bright screen on a MF camera do better?

Reading the Puts piece on RF accuracy makes me thing this might
be a complicated issue with a couple of variables, but I thought
I'd ask to get a general idea of the manual focus lay of the land,
as it were.

Much thanks.

Scott