Hi @James G.
I have formulated a couple rules I follow:
1. If I am going to live in a house, buy it with an investor mentality. Buy it at a cap rate that gives at least a 1% (hopefully 2%) spread between the fixed mortgage rate and the calculated cap rate (if you were to rent it to someone). This will allow the individual buying the house mobility in case they need to move. Factor in all your costs including maintenance, vacancy, and property management.
2. Double check that you can't rent for significantly less in the market you are buying in
3. Don't sacrifice on location when it comes to school districts, proximity to jobs, and crime rates
If someone can find something that meets that criteria I would have a hard time telling them not to buy the house. I think for someone getting started single family houses make perfect investments if they are bought at the right price. I also agree that if you want to scale as a professional investor that buying larger apartments will offer better returns. Also, the commercial lending aspects make it easier to grow since the property should finance itself after the down payment.