Proper sizing and installation are key elements in determining air conditioner efficiency. Too large a unit will not adequately remove humidity. Too small a unit will not be able to attain a comfortable temperature on the hottest days. Improper unit location, lack of insulation, and improper duct installation can greatly diminish efficiency.
More expensive does not always mean better, But you get what you pay for. You may save a penny on buying a cheaper setup, and end up paying double in fixing it, we will help you choose the right product.