Hmm, genuinely not sure who would win and I don't have access to the whole Batman One Million comic but I can find a few scans.
One of his abilities is to create fully sentient hardlight clones of himself that are totally independent and as capable as he is. In this image none of them is the original, his original body is actually in the Batcave upgrading the Batcomputer while his clones take on every criminal in Gotham simultaneously. They're independent enough that he has clones operating in our time while he's not in that timeline but operating in the 853rd century.
Batman One Million has a device on his utility belt that lets him rip a person's soul from their body and store it for later use, or transfer it (He uses it on Batman to put Batman into one of his cloned bodies.)
Based on the pre-event chatter, the Justice Legions regard taking down Elder Gods as a fairly routine operation. Fighting The Color From Space only requires Superman One Million and 5th Dimensional Superman.
His suit has a memory storage so large he's stunned Batman's Batcomputer only has 10,000 Gigabytes squared of data. Which is a really weird way of measuring data but whatevs.
Batman One Million's Martial Arts repertoire includes a psychic combat style used by some kind of advanced octopus, which lets him attack the psyche and body simultaneously.
Capable of Gravity Manipulation, which he seems to mostly use to fly. Not clear if he uses it for anything else but at the least, we know he can fly.
Tanks a body slam from Hourman then one-shots him before spiking Hourman with a drug that simultaneously takes out Hourman's powers and makes him more accepting of new ideas.
Tanks Firefly's flamethrower without issue.
Batman One Millions "Body Quotient" is 1201. The authors stated this is equivalent to IQ but for physical stats, with a baseline human having a BI of 100. That puts him at 10
1101 times human baseline average. This is somewhat supported in-comic by the fact that he's able to one-punch S-tier characters like OWAC (one-million version of OMAC, who can throw down with Superman and Wonder Woman) and survived an explosion that wiped out both the Martian Manhunter and Wonder Woman One Million.