It is! Although I think perfect constitution can easily pair well with any type of magic, enhancer/constitution magic is the best combination, lore-wise and game-wise. In gameplay, there's a hidden stat that checks your heavenly favor synergy with your magic type. The synergy helps in you awakening better magic tier as well as giving bonus damage while using the magic. Story wise, perfect constitution mean you have the most perfect body in the world, and constitution magic entire purpose is to strengthen the body, so both paired together is the most effective.
Well, enhancer is using magic to strengthen your body, so it's technically still matic. But, you can still use other magic, even if that's not your chosen magic.
As for the first question, lol it's definitely weird for me to rank my own creation, but I'll do it. ( It's my personal favourite, so you shouldn't take it seriously. )
Common : Disciplined
Uncommon : Regen or Relentless Vigor. It's a tie between these two for me.
Rare : Good-looking for the story and how you're one of the best looking people in the world.
Elite : Sage eyes for the look and story.
Supreme : Martial zenith mogs