It's not a strange question at all! I'd organise it like this, from least dark to most dark:
Rhain (Sun path version) > Aerona (Sun path version)> Rhain (Star path version) > Aerona (Star path version)> Emrys > Ikemma
All the routes have happy endings so they'll all have a few wholesome moments, but Emrys's and Ikemma's routes definitely have a lot more angst and struggle before getting there. As for Aerona and Rhain, some of their romance scenes change a bit based on whether you pick the Sun or Star path in Chapter 3, and Star will generally be a bit darker.
I hope that answers your question!