As a marvel fan, I'm sorry but you have to know the origins of Darkseid. He wins this one. All of the losses has been explained as his clones that he sends out to fukk with superman and still they win 9/10 times and his Omega beam is no joke. Superman is literally on Thanos level (yes, he's stronger than Odinson referring to golden age superman that literally lives in the sun) which is why the infinity gauntlet plays a vital role into Thanos strength.
With that said, Thanos is written way better with much more depth and there are plenty of more characters in the marvel universe that would wipe the floor with both Thanos and Darkseid. fukking squirrel girl beat Thanos. Lobo can beat Darkseid.