For me it’s definitely gen 4 (heartgold and platinum are just. top tier), but gen 5 is really close. Really polished and challenging games all around
I also think gen 7 is pretty underrated, especially USUM which got a bit of hate for being too similar to Sun and Moon. Which is kinda true…but I think the end result was pretty good all things considered.
SV is interesting to me because, i feel like at times it’s the best pokemon game (story, music) but at other tims it’s the worst (glitches, lag). I personally have it decently high in my rankings, but it’s weird how inconsistent it is lol