Theoretically Darkseid is more durable and powerful than Thanos with a greater host of innate abilities, but beyond this he's every bit the glass canon we find to be typical of the hyperbolous DC Cosmic arena. Both have been written inconsistently and jobbed hard so it's really hard to say what counts and what doesn't, but does one really surpass the other without the advantage of their native realities?

Both also have scapegoat clauses that account for inconsistent writing (Darkseid uses manifestations, Thanos uses clones), but while Thanos canonically grows stronger and stronger with the comics over the years, Darkseid varies by which iteration/DC reboot he hails from.

In terms of strength (ALE & Infinity Gauntlet aside), both are comparable. In terms of speed, Darkseid has the apparent advantage, though we've seen Thanos battle with characters who can fight and react at speeds comparable to Superman and to be fair speed is one of the most inconsistent and poorly measured aspects of both Universes, more so in Marvel than DC so it's something to be taken with a grain of salt.

So the real question is, which iteration of Darkseid is the most powerful, because many past versions seem more on par with Thanos than his most modern incarnation. Darkseid seems to have a greater host of abilities, but Thanos can't be killed by singing or a Bat-Bullet so it's really up to the writers honestly.