which one should i buy?

As far as i know you get more stuff with GOTY (2 additional characters and a lot of skin DLCs, might be even more) so if it's cheaper I think it's a no-brainer.

erm, is this a real question?

Psycho and Mechromancer - two great new characters, they are really worth buying/playing. I mean you should go for GOTY. It's only 2€ difference - if you'd like to buy season pass + 2 hunters, it would be +4€, at discount. At full price each character DLC would cost 10€.

Is better and cheaper buying GotY, but with GotY you won't get all the 1$ skin DLCs, the 5 Headhunter DLCs(but they're small) and nor the Borderlands 2: Ultimate Vault Hunter Upgrade Pack 2, which allows to level up to 72(all this DLCs I said before have to be bought separately), but with Season Pass you will spend similar or same and you will get less, only the 4 big DLCs, so you will miss like 5 DLCs that are included in GotY and not in Season Pass.