Depends on which games you focus on. I, for example, think that G4 was the worst gen unless you count the G2 remakes. However, if you count HeartGold/SoulSilver, you realize that they had pretty much everything that made the original games great and more, driving G2 further down the list.
My opinion:
Black/White > HeartGold/SoulSilver > X/Y > Ruby/Sapphire > Red/Blue > Gold/Silver > Diamond/Pearl
I haven't played the G1 remakes and haven't beaten Black/White 2, so I can't comment on them. However, I feel that the Pokemon games have, roughly, gotten better with time, with Diamond/Pearl being the chief exception due to its boring world and X/Y, despite being a perfectly fine game, being a lesser exception due to its stepping back from some of the things that made G5 great (lots of new Pokemon, interesting characters, cool themes, etc).
Love and tolerate.
