All of the Ivy League schools are going to be considered the "best" degrees for business management (notably Harvard and Penn). Non-Ivy League schools with fantastic programs are Duke University, Stanford, Northwestern, and Chicago. More economical (less expensive) schools with fantastic programs are Michigan, University of North Carolina, University of Virginia, NYU, University of Texas, and Indiana University.
Having said all of that, you do not need the best degree to start your own business. School will help refine your business acumen and life experience will help prepare you for this.