There are like 3-5 completely different family trees of computers in their numbering scheme (depending on how you count), all of them are notable in some way.
For software, the PDP-11 has an ironclad claim on operating systems (Unix - which gestated on the PDP-7 but was born on the PDP-11) and languages (C), with a strong 2nd place in hardware via its heavy influence on the venerable Motorola 68000 family.
I also agree the PDP-10 should be part of this conversation as it was certainly influential. My second-hand sense from reading retro history, is the PDP-10 was beloved, if not revered, by nearly all who touched it. It was indeed an aspirational North star, but its eventual influence was both delayed and limited. Limited because it was a monstrously powerful mainframe with an equally monstrous price, selling only 1,500 units compared to the PDP-11's 600,000. This limited those who saw it to major research institutions (MIT, Stanford, etc) and large corporations. And delayed because the PDP-10's incredible power allowed some futuristic concepts to be experimentally prototyped on it first, but the advanced operating system and networking ideas pioneered on the PDP-10 would have to wait for 32-bit power to arrive on desktops in the late 80s and 90s.
Personally, I give the nod to the PDP-11 for biased (but justified) reasons. Everyone in 80s computing knew of the PDP-11, whereas I was already a retro collector before I'd ever heard of the Datapoint and its valid claims to the title (and I still can't name its operating system or any languages and applications born on it). Unfair... but is history is rarely fair. And in any dead-even tie, whatever side x86 is on must lose because, to me, it will forever bear the WinTel beige stain of being the asteroid that snuffed out a Cambrian explosion of diverse platforms, OSes and apps in the late 80s to mid-90s.
