I can't imagine anybody with young children buying a house without heat. If you don't put in a central HVAC system you will be scaring away a large pool of potential buyers. Plus anybody with cardiac issues like me would want a place that would avoid extremes in temperature.
If you can swing it, get a combined HVAC and air filtration system. That would probably make it more attractive to anyone with dust and/or pollen related allergies, plus keep the place cleaner.
The rating system for HVAC systems is the Seer. I don't know how that was established, but I know the higher the Seer number the more efficient the system is. When I bought my first house, it came with an 8 Seer system. When the HVAC gave up the ghost, I replaced it with a 13 Seer system. Much more efficient.