For me it would be either Gaia or Brynhildr sizeable... assets. Brynhildr is kind mother-type/older sister-type while Gaia while creating similiar impression would crush anything that stands in the way of her lovelife (Be it worlds itself).

Their voices and appearance are great, but when it comes to scenes Gaia is losing to Brynhildr in that case (I really wish her second scene was something else...)

Plus I have them both. ^^