I'm not offending anyone but I would say ''git3 gau3'' is the right one. However, both of them are completely fine and u can say both. According to the theory, ''git3 gau3'' is the right one, however, I think more than 80% of native Cantonese speakers speak the wrong one unless those people who have studied a degree in Cantonese. How native speaker learning Cantonese is to 'hear and say'. We don't even learn the theory and some of the school don't teach the theory at all. People say it wrong day after day so it becomes more commonly to use. I personally say that words in the wrong way. I think only the fussy people will criticise you. Other than that, it's utterly fine to say the both. I'm not encouraging you to learn the wrong thing. It's what we call 'modern language' though.

Hi Yair, It is pronounced "git3 kau3"