Route 117, for two reasons; one is accessibility. There was also a Day-care located in Kanto's Route 5, but since we're comparing the one at the Sevii Islands, my statements will be based as such. Route 117's can be accessed fairly early in the game, (before you get your third badge) while on the other hand, the Kanto Elite Four must be defeated to obtain the Rainbow Pass that takes you to Four Island.
Unapologetic already mentioned the second point; an optimal path to "farm" your steps for hatching eggs. Very useful for nature/EV/IV/egg move breeding, especially with Flame Body/Magma armor + Mach Bike. To expand on that, it extended from the right side of Verdanturf's Battle Tent sign all the way to a boulder in Route 118. All you literally had to do was hold either the Left/Right buttons on the pad and your egg(s) would hatch in no time. It's also worth noting that unlike in Emerald, this path was much shorter and less refined in the original Ruby and Sapphire; the Contest Hall sign in Verdanturf was placed two-three tiles further to the right, and you would run into the top of the treelines in Route 117.
