I mostly work with multi-family properties myself, but have seen investors on both sides of this be successful. A lot of your decision to choose one or the other depends on your goals, your resources, your time, and your work ethic. I would take the time to visit your local REI club and try to talk with some experienced guys. You'll hear lots of different ideas and thoughts, but most of all you learn what makes sense to you.
REI isn't an exact science. Certain things work in certain cities and then completely fail in others at one time and then succeed at another time. So, learn as much as you can and don't be afraid to jump in when you think you're ready. As long as you have a good team around you, you'll be fine!
Oh yeah, I have single families now and they're working fine for me. I do very little on them and they make a nice return. I look forward to getting into multi-families in the next couple of months as I'm locating good deals.