I think that for most people, the 'better' route is whatever fits best with how they're playing their Champion(s). I doubt there's going to be one option that has radically more content than the other down the line, just different content. Like, I can see the next Kas encounter having a major shift depending on whether or not the Champion and Kas are romantic, with a unique sex option or two depending on which route you're on, but I don't see Hostile!Kas having substantially more content than Romantic!Kas or vice versa since that would kind of penalize players for picking one over the other.
Oh, speaking of which per the design doc there's three states Kas can be in (Hostile, Lustful and Romantic) though the first two ultimately lead to the same path in the dungeon with only the last leading to Wraith-chan and post-battle sexytimes. It seems like the options are locked-in once you hit the end of the dungeon. I imagine there'll be some variations in the future for the more middle-of-the-road 'Lustful' state as well, but the writers only know what the next steps are there.