I found, personally, in my admittedly still somewhat limited 100hrs between Switch and PC, that replaying the campaign on hard mode is the most fun, least full on grindy way of leveling. And on NG+ and beyond (even if you reset by switching to hard mode instead of using Godsbane) all of your port crystals stay put and you even get duplicates in all the old locations so you'll have twice as many on NG++ etc, so travel time becomes inconsequential. Aside from the hydra head quest, you can even teleport directly to escort locations and get super quick exp, not to mention being able to keep all the badge of vows in your inventory so you just grab them, run to the pawn guild board and watch the exp roll in a second time. I skipped a lot of quests due to auto fail or just not finding them on NG but even though I went back and did most of those, ng+ took me 25hrs as opposed to 60 for NG, and I went from level 40 to 68, slightly less than an hr per level is way better than what I got out of NG and IMO, way more fun than grinding the same big enemy over and over, picked up a lot of story stuff the second time too.
That being said, I also just beat Dark Bishop for the first time and gained two levels, so maybe BBI is definitely the way to go once your ready for some of the "real" big enemies? I still feel like I'd get incredibly bored with BBI doing that over and over from 68-200
