Tom Vs Jon, for a few reasons.
Alex still has work to do at 205. Ankalaev being the main one, I'm personally fine with him moving up after that, I think 3 defenses is the threshold.
Tom simply deserves it. He has 8 HW wins in the UFC. 5 top 10 wins, is the current interim champion and he deserves to try to unify.
It's a more competitive fight. Let's be honest, Poatan is just going to get Ciryl Ganed by Jones. If he doesn't catch Jon clean in the first 15 seconds it's a wrap. Guy was held down and controlled by Izzy, and Jones taps out black belts for fun.
Tom gives Jon issues everywhere and that makes it a competitive fight. He's bigger, younger, faster, legit black belt in BJJ, fight ending power in everything he throws.
Only 2 reasons anybody would rather see Poatan fight instead of Aspinall.
-Poatan fanboys that want to see him get 3 belts ahead of more deserving heavyweights.
-Jones fanboys that are licking their chops at the thought of Jon being gifted another guy that can't grapple and want to keep Jon as far away as possible from Aspinall.