If I went into most places selling cables I'd get laughed at if I took that
line, they'd say 'hie me to a research lab, if not an actual nunnery'.
Not
that you're wrong, but if you want a single general purpose cable for HF and
VHF especially if stocking it for general sale, then there IS a 'best' cable,
defined simply by that which most likely serves the wide range of purposes at
a low price. Currently in the UK that cable seems to be RG6; few places like
to stock more than one type for RF if they think one will do. Perfectionism
is NOT the first base. It's reasonable to expect some standard without being
told to either become an expert or use a bell wire and stay in ignorance. RG6
works, but they sell it for VHF/UHF, not RF. I'm not so concerned with
moderate losses, but SNR maintained by good shielding matters to me.
You seem to miss the point that one shop's RG6 (or most other RG cables)
may well not be the same as another's. So there is no definitive answer
to you question.
It is also very unlikely that 'good shielding' will have any effect on
SNR in most applications, other than due to increased loss if the
braiding is very very poor, or you are running the cable very close to a
source of broadband interference.
Jeff