Basic EFI Needs?
Speed Density is a system whereby manifold vacuum and air temp is measured to determine total airflow into the engine.
Mass Air uses a heated wire to determine the actual amount of airflow into the engine.
Common magazine groupthink on the subject is that "SD bad, MA good" based on the fact that MA allows you to make modifications to your engine without having to recalibrate your controller - it will adjust automatically to the increased airflow to a certain point. This is fine if you're modifying a stock engine slightly. Anything more and you have to recalibrate.
Mass Air is more complex than Speed Density in terms of the sensors required, plus the restrictions on airflow it has. If you're going to be playing with the VE tables in the computer anyway, SD is the simpler way to go in terms of setup and maintenance.
1969 Ford Torino GT Fastback