I'm a DDD main and use DK as a fun secondary. On release DDD was definitely better but he's gotten zero buffs

while DK has gotten a bunch.
I think DK is better right now. DK has better frame data, run speed, combo game with these recent buffs (although DDD's is still really good), DK punch, amazing bair, shield breakers and close to the same edguarding ability. The only thing DDD really has on him is recovery and the gordo. And the gordo isn't useful except for spacing/edgeguarding in most matchups and DK's recovery is workable when you get used to it.
I feel like DK's frame data and early KOs with cargo to upair on platforms make him better against the top tiers. And I feel like he's definitely better than DDD against campers because of his run speed.
I think DK is mid tier or possibly high mid whereas DDD is low mid or low tier. I'm much better with DDD personally but I think that's just because I've put way more time into him than DK.