Which company will be best for you will really depend upon a number of circumstances. There are dozens of companies offering student loans, and the only way to really know which is best is to apply and see where you can get the best rate. Here is a guide from last fall that should give you a good idea on what to look for and what to avoid: https://studentloansherpa.com/…..-freshman/

To answer your second question, variable interest rates are typically tied to an interest rate index such as the LIBOR or other well known interest rate. The exact way the interest rate is calculated can vary from loan to loan, but the important thing is that the interest rate changes with the economy. Right now interest rates are pretty low. As interest rates go up, the interest rate on a variable loan will also go up. If you get a fixed loan, the interest rate does not change over the life of the loan.