Damn, that would be a fantastic match. I'd say Jones until seeing Ngannou's performance vs Fury. The fact he actually went toe to toe with Fury in boxing only, dropped him once (twice if you count that one Fury smartly disguised into a slip) and arguably won the fight (imo it was handled to Fury because he's the champion and to save the hype of his match vs Usiky) means he's just unbelievable.
In a stand up fight Jones would be in the disadvantage, no doubt about that, despite his more versatile muay thai style with kicks and elbows... But Ngannou is just a tank, the man has a resilience beyond belief and a nuclear punch, which would have likely KO'd Fury were it with UFC gloves. Jones would need to take it to the ground. I think he can still stand up somewhat with his oblique kicks and grappling.
Ngannou is obviously disadvantaged in the ground... But he is no slouch in the ground either, he has proved to make big advancements defending from Miocic's takedown attempt and clearly outperforming Gane using wrestling when his knees were injured... And he kept training it. Obviously that doesn't compare with someone like Jones who has grappled and wrestled almost his entire life and was being coached by Gordon Ryan, but since Ngannou kept training wrestling, and has monstrous physical strength, never doubt this man's abilities in avoiding takedowns and holding Jone's impetus in it.
One thing that may be decisive is Ngannou being more of a natural heavyweight, his muscles seem more well built and more natural and imposing, while Jones has to fat up a little.
It'd be a hell of a match and could go either way, but still, if Jones is in good shape, well prepared for the battle and does it still when both are under 40, as a final GOAT battle, I'd favor Jon Jones. I think his complete mma skillset would give him the advantage vs Francis, but it's tough to choose. It'd be a match I'd be really willing to occur, and it'd the true battle of the baddest imo. I'd slight favor and pick Jones, but it's still uncertain as fuck. One momentum from Ngannou and a well connected blow, as well as a good and successful takedown defense could put Jones in huge problems. I'd say Jones 51/49, but damn, it'd be a hell of a match. Rooting for Jones to recover well and quick, defeat Miocic, maybe do some successful belt defense vs Pavlovich or Aspinall (which would still be a hell of a challenge to him... But I think a well prepared Jones can really take them out) and do one final one vs Ngannou. Or after Miocic do one vs Ngannou already.
Thing is, despite having more or less the same age, Ngannou seems to be in a better shape I think, he seems to me with best physical overall than Jones. But dunno, DC said Jones was kinda overloading himself with this new body of him which he isn't that used to, which led to the injury, and that Jones was wrestling harder before than the one moment which made him injured, which may hint at that body not being so ideal to Jones... I think this extra weight works very well for a solid take down, but Jones seems closer to me to have a better performance in a midterm between 93kg and 120kg, like 105kg or so. But still, solid mass would still be needed to take down and wrestle with a tank like Ngannou more easily and guarantee this advantage side.
Really tough to say overall, I'm still picking a well in-shape and prepared Jones, but still with many doubts overall.