PS4 Pro supports 4K resolution-enabled games (of course assuming you also have a 4K monitor/tv).
Performance wise, specs is obviously better compared to PS4 standard, but the performance will depend on the game itself if it utilizes the hardware boost for PS4 pro otherwise it will probably have the same performance w/ the standard one (Newer PS4 games will most probably maximize the performance offered by PS4 Pro).
If 4K resolution does not matter to you and you want cheaper, I suggest buy the standard one,.
