I generally recommend the heat pump version, as it is an efficient way to also heat the areas you are going to cool. Heat pumps are by far the most efficient way to heat a space with electricity but do lose heating capacity and efficiency in extreme temperatures. You may need a back-up or secondary heat source depending on your application.
As far as savings, a 23 SEER system will cost approximately 18% less to operate than 19 SEER system. Higher SEER systems may also qualify for a rebate from your utility or local authority (if offered in your area). This is a rough estimate as usage and actual savings will vary.