Seth has a combo atk debuff + a barrier on whole party. For most content, Seth will be way better than Sol. And if you face a boss that requires dispel, you can just take Cassio/CM as EX skill.
Imo, Seth, Amaterasu, SSR Nike, Cthulhu, Hades... have 3 excellent skills. Heck, even SRs like Oberon have 3 useful skills. Alfrodull on the hand is way too situationnal.
Sol is really cool if you're starting, especially with her heal and her Atk debuff. However, when you start considering miracle tickets, you should already have an elemental preference.
Picking Sol if you're main Water/Wind will not be "bad", but it will be far from being optimal.