While Route 7 is a nice place to chain, I found that different types of grass are easier than others (for me anyway), so I just wanted to add a few places.
Route 5 was the easiest for me, because there's a really square patch of purple flowers, just near Camphrier Town, that's really easy to chain in. It has Skiddo, Furfrou, Abra, Pancham, Plusle/Minun, Bunnelby, Duduo and Gulpin. Skiddo and Furfrou were easiest for me to chain because they have a relatively high encounter rate and it's really easy to tell their shiny versions. Plusle is hardest in that respect, as its shiny version has barely any difference and it's got a low encounter rate.
The Pokemon Village is another good place to chain as well, as there's a large patch of yellow flowers that's kind of square. It's near the Furfrou and Espurr running around. It's got Zoroark, Ditto, Gothorita, Amoonguss, Noctowl and Jigglypuff. I found yellow flowers harder to chain in though, because I just couldn't tell right away which patch was shaking fast/ medium, like I could with purple. Note that Gothorita is hardest to chain simply because there's nearly no difference between the shiny & normal versions.