I added a brief comparison of Sol, Amaterasu, and Gaia as versatile picks for rerollers (typically new players). Second paragraph is new. I didn't go into details because that would result in an extended discussion, character-by-character and element-by-element, that doesn't suit the purpose of this section.

Rerolling strategy to build a near-optimal team

What’s so great about Sol, Amaterasu, and Gaia?
Sol and Amaterasu are healers with strong utility skills, while Gaia is the game’s unique Paladin. Sol can heal + cleanse debuffs, dispel enemy buffs, and apply a unique -20% ATK debuff that stacks with most other -ATK debuffs. The -ATK debuff can greatly reduce enemy damage: 33% or more in some situations. Once awakened, Sol becomes a god-tier healer, capable of healing for 1800HP every 6 turns, cleansing two debuffs in a single cast, AND magnifying all healing by 1.5x every 7 turns. Gaia, once awakened, is uniquely able to nullify attacks on other characters, mitigate AoE overdrives, AND heal the team. Amaterasu can regenerate health + buff DEF by 30%, Blind all enemies, and apply a -20% debuff to both ATK and DEF.

Of the three, Sol is probably the most versatile and most likely to be a permanent member in a handpicked team, especially once she gets her Awakening in June 2018 or so. Sol fits into optimal builds for 5.5/6 elements (Fire is debatable), Amaterasu for 4/6 (Fire, Thunder, Light, Dark), and Gaia when core debuffs are otherwise covered (-Fire, -Dark).