In terms of cutting edge it has to be the B-52 IMHO.
To develop my argument.
The B-17 was the first of the “modern” four engined bombers – but it was limited by being designed as a maritime attack aircraft and had a bomb bay that it was impossible to enlarge.
So, it was always criticised for it’s small payload.
The Lancaster was very much a late 30’s design, but blessed with some good luck. It’s original engines (RR Vultures) were failures and it was fitted with four RR Merlins in nacelles designed for the Beaufighter – by some lucky chance they gave results well ahead of expectations. Also, the specification required the carriage of two torpedos – the resulting cavern of a bomb bay allowed the Lancaster to carry bigger bombs than any of it’s contemporaries.
Both the Vulcan and the B-52 benefitted from the windfall of German technology at the end of WWII.
But for the Vulcan, Roy Chadwick deliberatly chose a Delta design to allow him to use conventional construction techniques to build a bomber that handled like a fighter.
That huge delta wing was built with design techniques similar to the ones Boeing used in the B-17. it had huge internal capacity and a cavernous bomb bay
The Vulcan held the record for the longest bombing sortie for may years.
Boeing used German technology for swept wings, but also the use of podded engines to act as mass balances to keep wing structural weights down.
So, you can make a case that it was aerodynamicaly on a par with the Vulcan and structuraly at least a generation more advanced.
As a long-range bomb truck the B-52 is hard to beat – which is why it is still being flown by the grandchildren of it’s first crews.
Bit nobody, in their right mind, tries to barrel roll a B-52