This is one of those questions where I feel both answers are correct. I think Doom Eternal is overall the more satisfying experience and the better game from a mechanical standpoint, but for me, in a completely different sense, Doom 2016 is "better":
Timing. It was the right game at the right time.
2016 was around the tail-end of the hegemony of the modern military shooter, whose influence dominated the first person shooter for the better part of a decade. While never inherently opposed to them, I was getting really tired of that particular schtick, and it felt like many people agreed. In comes Doom, a franchise which many had written off by then, surprising everyone with A) being unexpectedly good and B) being in many ways the anti-Call of Duty. It says "Fuck cover, fuck health regen, fuck two weapon loadouts, fuck some dude blabbing in your ear giving orders, here's a gun, there's some demons. Get the fuck in there and don't stop until your arms are the skewers in a demon head shishkebab." Yes, near the end and especially on a second playthrough some underlying problems start rearing their heads, but that first time around 2016 was so refreshing and visceral.
That lightning in a bottle factor is something Doom Eternal doesn't have. It can't, by virtue of being a sequel and the moment having passed.