>>18094016Gen 1 is the one I have the fondest memories of, but that is obviously nostalgia. After the first gen, I found my enjoyment of the games decreased with each new gen up until 5. Black/White both felt very fresh, having only new Pokemon in the games probably helped that, and Black2/White2 I thought made revisiting old areas work and the flashbacks to Black/White events was neat in my opinion. Gen 5 definitely renewed my love of the main Pokemon games.
Gen 6 is also pretty great, and I believe it has the largest amount of Pokemon you can get without needing to trade with other games. They also made breeding the perfect Pokemon easier if you ever decide to go down that path. The game also feels a lot more modern than the other games were of their time, and I personally love the music from X/Y over the other games.