I find that Shadowheart lacks that shallow charisma (i.e., good looks) that I found appealing in Morrigan.
Weird, because I think Shadowheart looks a lot better. She also has a lot more character to her while I found Morrigan to be a far shallower sass machine. Morrigan always appeared as though she wore makeup and skimpier clothing, not sure if maybe that's what you found more attractive?