I'd say it's best to combine your seal-earning with other things.

- Roll on drops from dungeons while you do your roulettes. i70 gear will net you ~800 seals and i80 drops from the new dungeons will net ~900.
- Earn seals while doing FATEs and grinding atmas for your atma or alexandrite for your novus.
- Do guildhests while farming commendations for your gold magitek or going for the guildhest achievement.
- FATEs are good ways to grind out enemies for your paragon's gown (reward for 3000 FATE achievement) and butcher's crown (reward for 100,000 kills achievement).
- Level your crafts and turn stuff in when you can, for supply missions at your GC.