Best is a subjective term. To some, best may be using their own money since they wouldn't have to rely on someone else or pay interest. Some may prefer to borrow at low interest for additional leverage and use their own money to fund new deals. It would ultimately depend on your financial situation. You can get a rehab loan from a hard money lender, a personal loan from a bank, find a private money lender, or ask friends/family for assistance, or even wrap the construction loan into the mortgage via an FHA 203K loan or HomeStyle Renovation loan from Fannie Mae.