If you don't have a lot of credit history or your credit is poor, it may be easier for you to get a loan from a private lender. If you have a good credit score or an established relationship with the bank you want to borrow from, you will likely qualify for better lending terms from a bank.
Both banks and mortgage companies can make mortgage loans. Banks, however, can also take deposits of your money, which can be placed into a savings account or checking account, but mortgage companies cannot take deposits.