First determine the size of the refrigerator that you will need. An over sized refrigerator will not only cost more to run, but will also be less efficient if you do not have it packed to almost capacity. This is because each time you open the door, there is more air space that loses the cold air and has to be replaced.
When you're refrigerator is full, the coldness of the food remains at the temperature which was before you opened the door, thereby requiring less time for the cooling cycle.
So it goes without saying that a large unit for storing smaller quantities of food will not only cost more to run, but will run longer each time you open the door.
After determining the size, you have the energy star label for which to help decide which unit will perform using the least amount of power over the year under normal use. These labels are easy to understand, and it's a matter of comparing each for their ability to keep food cold using the least amount of energy.
Go online and look for reviews for each of the units you would be interested in. There is a lot of information out there which is very useful for determining which unit to buy.
Also, make sure that the store you buy the unit from has a price guarantee that assures you that if you paid a higher price, and the unit goes on sale in the next 30 days, you will be refunded the difference.
Don't buy what you will not use. Icemakers and water dispensers add to the cost as well as using more energy. So think about how much you may save for the little bit of inconvenience for using ice trays and a separate water filter for your water faucet.
Energy efficient refrigerators are a lot noisier than the older types, and don't be afraid to ask about the noise level each may produce. Some make less noise than others.