It depends on what Pokemon I want. =p I started out with shiny Shinx, and I got to 40 once, but then I broke the chain. ;; Later in that week I tried again and got it up to 47, and got five shiny Shinx as a result. Then I wanted a blue Ponyta because I thought the blue flames looked so cool, so I chained them non-stop and eventually got four shinny ones. That was it, though; the others chains didn't work out... ^_^"
Nowadays I don't chain, though. It takes too long and the natures aren't guaranteed to be great. I hatch shinies with the RNG instead.
::EDIT:: Oh, I wasn't being specific, heh-heh. Route 202 for Shinx and the place above Oreburgh for Ponyta.