which FATEs give the most GC seals?

[Hasrat]

If you have dungeon/tome gear, you can trade those in for seals. The higher the level, the more you get and it's way faster than doing FATEs.

Remarkable. Even after 2 years, people still can't read two whole sentences.

Tip: When people are asking this exact question, the reason is typically because they need seals to rank up to the point where they can start turning in gear. That isn't a default option.