Which job offer to choose?

Few weeks ago I did an interview and I was chosen to company A, the company is a public sector. I singed the contract and the starting date is in 4 days. Yesterday, my ex company wants to join their team. I really want to join them because I know them very well and I know how they work.

What shall I do? Shall I go to the first company? Or choose the second company? If I choose the second company how I am going to tell the first company?

Asked Dec 18, 2014

TIP: If it's not your answer to this question, please click "Leave a Comment" button under the question to communicate with the question owner.