I see Evelyn as far superior to Moonsong, for many reasons.
1) She's been there since their childhood, so they've developed a deep bond of friendship, and even love behind it all.
2) Later as they progress, she drops all her limits and tells the MC she'd do literally *anthing* with him, and encourages other girls getting on board.
3) Moonsong wants a casual-only relationship. Evelyn probably loves the MC (and he her), but still doesn't care about other girls.
4) Evelyn considers herself the Harem Alpha, but doesn't try to control the MC or who he is interested in.
5) Her body is more voluptuous than Moonsong's, but not "thicc" at all.
6) She's highly motivated to please the MC, probably due to (reasons), but she remains herself under all of it.
Sure, I still really like Moonsong, her energy, her sexual openness, and everything else. But she doesn't bring as much to the table as Evelyn in my mind.