Vat or cst

We are in the business of Preparing and supplying display panel to various customers located at different places in India. My question is should i charge VAT or CST if i supply the same outside my state, because the same work is done in my state and we go and put the display there.

What if the customer are from different state and put up an event in my state, since in the invice the address would be of a different state. What should i charge VAT or CST ?

Thanks

Mukesh