I recently got my H1B petition approved and have not got Visa stamped yet.I have a question regarding validity of visa stamp after switching Job.

For example I am working on H1B for company A and have valid Visa Stamp with company A cited as my employer.
If now I switch to company B (ie transfer my H1B visa to new company) ,do I need to get new Visa stamped again at a US consulate if I go out of US or I can enter US again with previous Visa stamp(on which company A is mentioned as my employer).

I am concerned with the issues which I can face at port of Entry while re entering in US. With respect to this point
What would be more advisable to get VISA stamped first and change job later or it would be fine to change job and go for visa stamping later.