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.
]Journey to the West Event Re-run
Hunting Quest Part 1
Fate/Accel Zero Order Advance Campaign
Fate/Accel Zero Order Event
Lostbelt No.1: Anastasia
5 Star Servants Tier List: Best Servants [4/13 updated!]
Best Servants [★4]: 4 Star Tier List
1-3 Star Servants Tier List
Best Craft Essence: Craft Essence Tier List
Ivan the Terrible (Ivan the Thunder Emperor)
FGO Reroll Tier List
Anastasia Nikolaevna Romanova
Irisviel (Dress of Heaven)
Ramesses II (Ozymandias)
Black Holy Grail (The Black Grail)
Talk on the Heated Sands
Nine-Headed Bull Demon King
Lunar Hot Springs