P4G has a better story, overall setting /atmosphere and some more interesting characters. P5 has better gameplay and dungeon design.
The gameplay in both is just bland and kinda bad, dont know how the series gets away with this till this day. Say what you will about FF combat, but at least they are trying to do something new and I actually liked XIII and VII Remakes combat.
P4 also has the most boring dungeons of any game I have ever played. P5 is still boring in that regard, but is a bit easier to take in, since its not all randomly generated. Then again P5 has a huuuuge randomly generated dungeon just for busy work.
Both games suffer from the fact that they are way too long. The gameplay just cant carry them over the finish line. Personally I would prefer the combat of P5 Strikers. Make it more in depth, add more RPG elements to it and make it even more visually appealing and I think we could have something here. Also, just trim of all the fat. Less grinding, more actual challenge.
While of this does sound very negative, I do like both games a great deal. Its just after spending over 100 hours on them, you notice the lack in gameplay variety a lot. P5S on the other hand felt quite good at about 40 hours. I think a full Persona game could clock in at about 50 to 60 hours and all would be fine. the other 40 hours is just grinding in randomly generated dungeons anyways.