It depends on the shiny but i recommend horde hunting since all you need is a pokemon that knows sweet scent and if you use it outside of battle it will spawn a horde of five pokemon which is pretty fast

ok thank you

Hordes were already mentioned in this thread, and that's great for Pokémon that appear in hordes! For other species, the Poké Radar increases shiny odds when chaining! Good luck out there :3

Chain Fishing is the easiest and fastest method. But you can only get fish pokémon. Other than that friend safari is pretty easy and has better odds than hordes in case you don't have the shiny charm. The horde encounters are really only fine if you have the charm.

Also PokéRadar chaining can be really fast, but at least for me it's pretty nerve wracking as you can lose your chain very easily... It's overall the most complex method I'd say.