I see two main branches. (1) Stories and (2) Better EpA.
For (1) strangely enough best stories in FL are free, but you may search for polls conducted every year and across all time to pick among the best (like this [Survey] Your favourite Fate-locked stories (January 2024 edition)). Some stories are particularly good not in literary sense, but because of lore for specific factions or events.
For (2) mechanical advantage long term (assuming you are planning to play for years) surprisingly small things give the most. Fate locked upgrade for Lab (especially if you are not super late in the game), cartographer for Stacks, specific ending of Your Aunt story (if you draw cards mostly in London). If your aim is more short-term, for example you need a lot of echoes to finish your Ambition or get some vanity item like Hellworm, you may consider buying few FATE locked items to allow 100% efficiency on some high EpA grind. Illegal device is not a bad choice too since you get +4 companions with advanced stats and sometimes very good side-options, and next year it will pay again with another 4 companions.