Reg 1 and 2 are from US and UK so Taxation and Duty makes it expensive when imported to Pakistan, while Reg 3 is for Asia mainly manufactured in China. So it's a lot cheaper to us. Otherwise there is no difference in quality of the console, all are made by Sony inc.
Plus there is no restriction on playing any region game or acquiring dlc of different region and you can make any region account like UK, US or India etc.