SEER stands for Seasonal Energy Efficiency Rating. The higher the SEER rating/number the more efficient the HVAC system will be. However one has to take into account the cost for a high efficient system vs the energy savings. You should take into consideration the estimated time you plan to live in your home and how many years it will take to break even on your investment "cost of equipment vs energy savings".Two-thirds of all homes in the United States have air conditioners.
Air conditioners use about 5% of all the electricity produced in the
United States, at a cost of over $11 billion to homeowners. As a result,
roughly 100 million tons of carbon dioxide are released into the air
each year—an average of about two tons for each home with an air
conditioner. Switching to high-efficiency air conditioners and taking other
actions to keep your home cool could reduce this energy use by 20%–50%
Some information obtained from the U.S. Dept of energy web site. eere.energy.gov/