BW2's story is by far the best of the franchise.
It gave us so much background information, great characters and a villain team that was well thought out for once.
Storywise;
5 > 3 > 1 > 2 > 6 > 4
Gen 1? that didn't even have a real story and not even that tiny bit on the Sevii islands had enough,
Gen 2, 4 and 6 had definitely better stories especially the latter 2
that didn't even have a real story and not even that tiny bit on the Sevii islands had enough, 
