Both has its pros and cons. Doing job helps to understand how organization works , how things operate on the ground whereas in post grad you get to study about the academic part of it , on what principles things operate. Its how you present yourself in the given choices makes the difference
This is what I think, it's better to go for a job based on UG degree and to the PG simultaneously or sometimes later, according to the convenience, this is what I am going to do, my course would be ending after 6 months.
Going for a job would be better after UG because sometimes one is not sure about their field of interest and even if they are pretty sure, then choosing the right course needs some time which one get when they take some break after their graduation. This gives some work experience to the person and the person will not be categorised as a fresher after their post graduation.