depends on how much $$ you have and how involved you want to be.
if you have a pretty big bank roll (around $1mm) id buy a number of single family homes around $200k and rent them out to families. the mortgage would cost you about $1100/mo plus property taxes, etc, but you could probably rent it out for $1800/$2000/mo.
property tax and interest on the loan you can expense on your taxes. at the end you will probably make around $2k +/- per month depending on property taxes and dues.
likewise, you can buy a couple 4-plexes in the city, but most people who live there, treat like like shit. my friends mom owns one and people destroy the place regardless of deposit and their credit history. although, she does make more than if she bought a few single family houses.
plus, the more tenatns, the more you have to. 4 4-plexes vs 4 single family homes is 16 hot water heaters vs 4. likewise thats 32/16 sinks and toilets vs 8
IMO, i value my time and dont want to be spending it all fixing up some unit for the next tenant to fuck me. people who rent single family houses are more proud of where they live then complex renters... says my friend who owns a number of each
edit: btw, a little added rep for my awesome advice, ill be gladly to take lol
