There isn't a comfirmed best way to do it, as some are better than others but only work on a select group of Pokemon, like chain fishing.
I would say that chaining with the Pokeradar is the most frustrating of them all to try and get a shiny on, as your chain could easily break. So whatever you do, don't use this one if your newish to Pokemon (like me! :P)
Chain Fishing is a really good way of getting a shiny. Just grab an Inkay with Suction Cups, a Super Rod, and bob's your uncle. However, this means you can only catch 'fish' Pokemon.
In my opinion, I would say that finding a shiny from a horde is best, as in X and Y, the chances of finding a random shiny was increased from 1/8192 to 1/4096 twice as good. In a horde, you battle 5 Pokemon at a time, which means you now have a 5/4096 chance of finding a random shiny, which simplifies to 1/819. So grab a Pokemon with sweet scent, because if you use the move outside of battle, you will always battle a horde if there are any!
That's only 4 time less likely than using a pokeradar and you haven't even began to chain yet!
I would say to use a combination of chain fishing and hordes.
Hope this helped!