Imo they both have strong points, stellaris is nice and shiny and new and appeals to a more broader audience. I like stellaris purely for its exploration of science-fiction concepts, like ringworlds, dyson spheres, eucemenopolis, orbital habitats. Stellaris also emphasizes is more of a culture/ideology vs itself.
I absolutely despise how shallow the combat system is though, and how basic everything looks. Stellaris has better 'sci-fi' overall.
Distant worlds truly shines here, while its scifi is quite dry like Starwars, it makes up for it by intricately detailing every little bit of logistic in the game, every little demand MUST have a supply and it graphically shows this, waging war in distant worlds is also so much fun, where fleet vs fleet doesn't just mean who has more 'fleet power' but who can put the best ship captains in command of the enemy ships, who can coordinate with strike forces and raiding ships to cripple an enemies military fuel depo's etc. This detail is what makes distant worlds special for me.
Now, if they can integrate good science fiction narative into DW2, it may well possibly be the best 4X ever made in existence (assuming it is what the devs want it to be, DW1 but just 'better')