In this specific situation, if it is the same game, I will always pick up the PS4 version over the PS3's simply due to the fact that I like the PS4's controller a lot better than the PS3's.
In other situations, however, if I need to choose between a generic PS4 title like, let's say, Days Gone or a shooter such as Seirei Senshi Spriggan for the PC Engine, with both being sold by the same price, I'd definitely go the retro way!