The lack of consensus is interesting. Different folks seem to want
different things from DIY outlets.

I would always do a compare between B&Q, Screwfix (or B&Q Lite, in
fact) & Toolstation for branded items where I know what I want and
only price/availability matters.
For timber, I'm sure that good specialised suppliers are better. In
my experience their wood is stored better and since they only sell
wood, it has to be of good quality.

The places I avoid, unless very desperate, are the local outlets of
the national builders merchants - silly prices with the good prices
reserved for trade accounts that allow "tradesmen" to bill the full
price to their customers while pocketing the difference. People slag
off the B&Q staff but I think these other outlets recruit the people
too dim for the big sheds.
Example: went into TP for an item that I'd seen for £12 in the
Toolstation catalogue; £18 was the price at their till. When I asked
if that was correct the price dropped to £13! The £1 excess was about
right for the petrol saved in not driving to TS. I suppose that's how
TP stays in business, it can't be service or the with of its staff!

Worse still are local builders merchants with such as "the 20% re-
stocking" charge when you have over-purchased and need to return
bits. Nobody has mentioned how flexible the much maligned B&Q is
when you need to take something back.

There's no one answer, you've got to work at it to get it right.
Naffer