There are a couple of nuances for this fight. Doomsday, despite being a comic book brick who can't even fly, is deceptively versatile at least as far as durability is concerned. He basically tanks any offensive option Cell has to offer but at the same time he has no easily accessible means of killing Cell except for grabbing him with superior lifting strength and bodyslamming him into a star while pummeling him into mulch.
Cell, on the other hand, has way more overt advantages. Since speed is equalized, he handily takes close-quarters combat. He's far smarter and his ability to fly as well as having several ranged options gives him far superior control over the battlefield. One thing I fear people tend to overestimate is Cell's Zenkai boost potential. It's honestly not that great. When Vegeta lasered him in half with the Final Flash he achieved no Zenkai, same with Goku using the IT Kamehameha. DD has no offensive abilities comparable to a DBZ-style laser so any damage he inflicts will likely not result in Cell boosting.
However, this is where I would have to give the edge to Cell. Namely for 2 things: Telepathy and the Spirit Bomb. Since several characters have demonstrated telepathic ability and Goku can straight-up read minds by touching people I feel it's safe to assume Cell could do the same. If Cell were to read DD's mind and learn how his power works, he would know that pure positive energy is something he's never survived before (AFAIK). So that's a much more accessible win condition.
Given Cell's superior intelligence and MUCH more versatile ability set I find it much more likely he would do this before DD could take him to a star.
