At today's rate.. for I Bonds if you buy a 50 dollar bond and will pay $70 at the end of the 20 years with EE bonds you will invest $50 and get a guaranteed $50.00 it just makes more sense. Because the E bonds are fixed.. if the I bonds ever go up in interest rate you could cash in the EE and put in I bonds.. but at .2 % ( point two percent) for I bonds NOw EE is the way to go.