6th Singularity Camelot: Land of Emptiness free quest is the best AP & time-saving location to farm Meteor Horseshoe. You'll get about 4~5x Meteor Horseshoe by spending 220AP.
3rd Singularity Okeanos: Caldera Island free quest is the first location you can farm Meteor Horseshoe.
Here is a list of servants that need Meteoric Horseshoe to perform Ascension and Skill Up.
Rashoumon event (Ibaraki Douji event)
Murder at the Kogetsukan
Inheritance of Glory
FGO Reroll Tier List [5/11 updated!]
Device Transfer Guide
How to farm EXP cards & level fast
Best Craft Essence: Craft Essence Tier List
Talon of Chaos (Claw of Chaos)
Glassful Sweet Time (Glass Full Sweet Time)