Both are pretty similar i will say, same AP 3120 caliber which a lot of people described it as one of the best in house movement in the world which i totally agree.
Well, i think it boils down to your wrist size. If yours is above 6.5" and if you are so used to Panerai, then go for 15400 instead of 15300. if u think panerai is too big for u and u can barely wear says submariner cos your wrist is around 6" then 15300 will probably fit you more.
I will personally go for 15400 because i dont generally like discontinued model save and except very collectible and or special edition model. 15300 is not collectible so I will go for newer version. Also, i think 15300's 39" is not "man enough". U know what i mean if you comparing RO and ROO.
15202 cost around 20% more than 15400. Moreover, I think the production is much lesser and hard to come by. 15202 is not my cup of tea cos it doesnt have a second hand which i like. Also, its carrying AP2121 cabliber which was licensed by JLC (historically it was partly owned by AP). I wont pay premium for non in house caliber since AP has produced a better inhouse caliber with 60 hours power reserve now.
Well, going for APROO diver is different ball game altogether i will say cos diver is ROO and not RO. This is akin CLK and C class which is in different water. But having said that, after bought the diver, now I am seriously considering 15400 which is like a 4 door sedan car which is very good for daily use, not to mention transparent backcase where one will get to admire the beautiful movement.