For me, it's something like:
P4G > P5R > P3 > P2:IS > PQ > P2:EP
P5 used to be firmly in 2nd place but the Royal content really narrowed the gap. I was very impressed with how well it was integrated into the early story and I really enjoyed the new character and ending (I was kinda meh on the original ending). P5 also has an all-time great game soundtrack.
I haven't tried P3 Reload yet; it went way down the wishlist once it became clear Kotone wasn't going to be in the game. I bounced off of P1 and P5T, so not sure on those.