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
5 Star Servants Tier List: Best Servants [5/9 updated!]
Best Servants [★4]: 4 Star Tier List
1-3 Star Servants Tier List
Best Craft Essence: Craft Essence Tier List
Minamoto no Yorimitsu (Berserker)
Ramesses II (Ozymandias)
Sakata Kintoki (Rider)
Holy Night Supper
Golden Sumo ~Rocky Area~
Victor from the Moon