* Full Disclaimer, I think both strategies are the safer routes of R/E investing the others because multiple tenants paying into one property.You will need to decide for yourself what is the best route.
MF) Pro= Everyone needs somewhere to live and not everyone wants to or can afford to own.
Con= Equipment breaks ie heater-pipes etc, usually at a bad time and you or property management co. has to arrange to get repaired quickly.
SS) Pro= A lot of people have more stuff then they can fit into their homes. They need somewhere to put it. Except for maybe the manager, no one lives on this property. (no 2 am phone calls)
Con= When money gets tight, usually people will skip paying their storage fees first. Depending on the state, this may be a small issue or a big issue.