I can only go off of personal experience, and have only sampled BA in Y, WTP and F (haven't yet managed a flight in CW). Here's how I would rank, based on my past few years of flying (I tend to give the greatest weight to hard product, as I value comfort and ability to sleep on overnight flights):

F Cabin:
CX (77W and 744, great in all respects)
KE (A380, great product)
AF (77W, seat may not be the newest, but it's comfortable, and food/service were terrific)
UA (77E and 763, great seat, and service is hit or miss, food is J cabin fare)
CA (77W, Seat is fantastic, but service was poor and food uninspiring)
BA (NF on 77E, generally good service, but that seat is tiny for F)
LH (Old F on A343/6, 744, A333, always love the service, would love to try their new F)

Biz (slot in BA wherever you like if you're familiar with products below, as I'm not in a position to judge CW yet):
BR (77W, Dom! & reverse-herringbone)
CX (77W, reverse-herringbone)
LA (763, prefer this seat to UA's enclosed pods, due to my height and ability to stretch out)
SA (A346, See LA comment above)
UA (sCO 77E/764/752, select a bulkhead for a larger footwell)
QR (77L, best of the angled-flats)
ET (77L, decent angled-flat)
AF (77E, decent angled-flat)
NH (77E), KL (744 - old product), LH (old product) - lousy angled-flat
SK (A333, lousy angled-flat and mediocre to poor service)

WTP - To be fair, I've only sampled proper premium economy products from BA (old WTP) and AF (on their 77W). WTP is far and away a better product than AF. AF's seat is awkward, has thin padding, and is simply not comfortable when reclined in the hard shell. I don't intend to pay for it again unless I can be assured of an upgrade to biz.

I'm looking forward to trying QR F and QF F in the next few weeks (and also have another upcoming BA F flight), so will have additional points of reference in the front cabin. However, based on my recent experiences, I'd rate BA overall as a good (but not great) airline. If the price is right, I'll buy an itinerary that includes BA, and will soon earn Gold, but it's not an aspirational product that I seek out over other options regardless of price premium.