First decide if you want 110 volt or 9 volt smoke detectors.

The National Fire Protection Agency (NFPA) has updated codes to require that new homes be equipped with hard wired 110 volt smoke detectors. This permanent wiring feature provides a constant, 110 volt power circuit directly to the smoke detector, thusly eliminating the risks associated with not installing or not replacing batteries.
110 volt smoke detectors need power to operate under normal conditions. They also have a battery back-up for the system during a power outage.
The standard 9 volt smoke detector, if checked and maintained regularly, is sufficient.
Next, determine if ionization type or photo-electric type would be best for your home.
Ionization smoke detectors sense invisible fire particles (common to fast-igniting fires) faster than photo-electric detectors.
Photo-electric smoke detectors sense visible fire particles (common to smoldering fires) faster than ionization detectors.
You may want to have an even mix of ionization and photo-electric smoke detectors throughout the home.