For me, best to worst:
DPPt > BW > GSC > SunMoon > RSE > XY > RBY
1. DPPt scores a win for me particularly in Platinum (which amended a lot of issues with DP) because of its featured villains and lores of the legendaries despite the lag issue, the wholesomeness of the three starters are also saving graces for me, Cynthia and Cyrus are both my favourite characters of Pokémon franchise, Sinnoh Underground was an interesting concept for fossil and evolutionary stone hunts.
2. BW has inarguably strong plots, introduction of interesting and charismatic characters such as N and Colress are pluses for me and pokemon introduced in gen 5 are still relevant even in current meta
3. The continuity between two regions started here. I also love the different means of transportations between two regions (transit train, S.S Aqua and your own flying pokemon)
4. A region with league in its early stage without a champion and kahunas in place of gym leaders definitely injects new life into pokemon franchise, it opens a whole lots of possibilities for the future of pokemon franchise
5. Gotta love Battle Frontiers and Steven
6. The few things I like about XY are the Pokémon Amie and mega evolutions
7. RBY fell flat when every gens after them had much more to offer, I really don't get first gen genwunners