It is an impossible question really. How do you do say whether a winger was better than a prop, especally in the days of specialism and competitive scrums,
I don't think many of us would able to comment on pre-WW2 but I guess some of British RLs best players came from that era.
As someone who started watching as a child in the early 1960s I just missed out on the best years of a number of the British all time greats. However, I once asked my dad the question and after a few moments reflection he said Brian Bevan. Objectively, he was the best wing man of all time and one of the / the most exciting player of all time with ball in hand.
As I said though, there are many facets to RL and finishing (even as I understand it often from your own in goal area!) is but one. Neil Foxas always a player I admired and arguably the best all round British player? A sort of Daley Thompson - superb at everything, but not necessarily the best centre, best tackler, best kicker, etc of all time.
Then there are those players who coud control and dominate a game themselves, Murppy, Fulton, etc and those who could produce the big play when it mattered - Fittler, Lockyer, Meninga spring to mind.
Then there are all those comparatively unrecognised players that set the platform to win games. Maqybe the best players of all time have been forwards? In my time some of the best forwards have been the unheralded ones - those who do the hard work quietly - never missing tackles, not making mistakes, but rarely doiung anything flash. Maybe one of those is in fact the best player or maybe to be a great you have to have that something extra to turn a game?
How do you choose?