This situation can be used to understand the elusive thing called "Luck". Luck is nothing but how we respond to an oppurtunity. The oppurtunity here is the offer an individual got from companies A & B. The best response in my view would be to take out time, think calmly and dispassionately about the details of both the offers and jot them down on a piece of paper. This should include remuneration, work atmosphere, growth potential, career prospects, working hours, ESOPs, holidays, shift from a city and even minor things like daily commute. After carrying out this exercise reach an informed decision and choose the company which offers you the best in the present and also in the future. If it turns out to be company B, call up Company A, APOLOGISE AND INFORM THEM THAT YOU WILL NOT BE TAKING UP THEIR OFFER. NEVER EVER USE THE OFFER OF COMPANY B TO LEVERAGE WITH COMPANY A EVEN IF YOU DECIDE TO GO AHEAD WITH YOUR INITIAL CHOICE.
