Right now they both do the same thing, but they have very different origin stories. Premiere started out as strictly an editor, and Resolve as strictly a color grader, and that pedigree is still pretty apparent today.
I prefer to edit in Premiere as the UI, controls, and integration with After Effects and the Adobe suite is hard to beat for my workflows. But the Lumetri color tech built into Premiere, while good, leaves a lot to be desired when you get serious about color work. It's usable for sure, but I run into its limits frequently.
Resolve just slaps when it comes to color grading. Nothing else (affordable) touches it. And sending my Premiere projects over to Resolve for grading is worth the round-trip for projects where color grading is important, or I can't trick Lumetri into doing what I need it to do.