Hey there,

Gate and cat both are a decent examination for pursuing the further education after your bachelor's degree. Both requires a good amount of preparation along with the smart work. Gate will be totally based on the engineering study that you have done throughout the entire 4 years of your BTech on the other hand cat is totally based on reasoning. 

You can go for IIM through cat only.

I hope you have got the answer.

Good luck ahead !

Now coming to your question,

Usually this B-School graduates work for BIG private firms, MNCs and Startups

The basic comparison is between this private MNCs and PSUs, when we talk about GATE and CAT now a days.

It is solely your choice to opt for what kind of life style you want after your studies, both of this options have pros and cons

After MBA from Good Institutes

PROS

You may get lucrative packages

You may get good corporate life style

You may get good exposure with in country and International as well.

CONS

Life may be bit hectic, which may disturb your personal life

You may have to keep running always, as job security is always a big concern.

PSUs through GATE

PROS

Job security

Good personal life with good package

Your work is directly associated with nation’s interest.

CONS

Time bound career growth

Monetary growth is quite slow when compared to other big private firms.