The fight is comic book Future Flash, Barry Allen, vs Reverse Flash, Eobard Thawne.
The way I see it is both are faster than current Barry because FF has blue lightning and RF has the negative Speed Force all to himself. So, they are almost evenly matched in terms of speed.
Both are from the future: FF was from 20 years into the future and RF is from the 25th century. So, obviously time travel is not a problem.
Both are highly clever in science and tech: FF made a suit that could regrow a hand. RF was a scientist that replicated the lightning strike to grant himself super speed.
Both are knowledgeable in fighting techniques: among other moves, they both use hand vibrating.
And lastly, both have demonstrated they are capable of killing.
You have the comparison. Feel free to include anything that can support one over the other if I missed something.
So, in a battle to the death who wins?
(And no time remnants allowed)