The interest rate is one of the major deciding factors when comparing accounts. The rates of interest paid into savings accounts by banks and credit unions can vary, based on the prime lending rate and other financial indicators. However, you can expect the rate fluctuations to essentially cancel each other out. Assuming a constant interest rate is the only way to compare different accounts to invest your savings, as you'll never finish your comparison if you keep changing the rates on your list!

If you use a financial calculator to estimate how much your savings will grow through compound interest over time, you must assume a constant annual percentage rate (APR) of interest. These calculators will allow you to input the amount in savings, plus the interest rate. It will then predict how much money you will accumulate over time due to interest.

Compare rates for money market accounts and traditional savings funds at websites like MSN's MoneyCentral and CNN's CNNmoney.com. You may find that internet-based banks like ING Direct can offer higher, more aggressive savings interest rates, because they don't have the overhead of owning or renting a building, and all the expenses that entails.

The APR is a major deciding factor, but not the only one. When searching for the best financial institution to invest your saved money, consider whether a minimum balance is required to open the account. In order for you to get the highest rates of interest, some banks require you to open one of their elite accounts, which may require a minimum deposit of several thousand dollars. Most people don't have this initial investment to make. Service fees on the account may also depend on maintaining a minimum savings balance in your account.

To get the best return on investment (ROI), look for accounts with high interest rates, low fees, and low minimum initial deposits. Finding this combination of financial factors will make you glad that you took the time to compare savings accounts in which to invest your cash.