Quoted By:
Gen IV online
>all random online interactions are located at Jubilife/Goldenrod, friend interactions and minigames are at any Pokecenter
>battling is restricted to friends on the base cart, but trading works with anyone
>Pokemon Battle Revolution is necessary to battle random players
>foreign Pokemon get bonus Exp. and can be used to breed for shinies, rewarding players for trading with people from afar
Gen V online
>all online interactions are located at the Pokecenter
>random battling is introduced, along with GTS Negotiations
>Join Avenue in BW2, giving bonuses for communicating with other people
Gen VI online
>PSS introduced, allowing for players to communicate at any place in-game, and stay connected even as they adventure/breed
>chat system, allowing players to let everyone know what they want/need or just have a basic status message for a personal flair
>profile pictures that easily tell apart XY and ORAS players
>GTS Negotiations replaced with trade requests, however, emotes have been removed
>GTS now allows players to search for Pokemon by name to get a certain species they've never seen before
>Pokemiles reward players for trading with people from afar, just like foreign Pokemon
>Secret Bases are now shared through the internet, rewarding ORAS players for connecting online
It's a huge step back from Gen VI's online, which is a real shame. However, it's not the worst, that would go to Gen IV's, and even then, it's justified in being the first.