Where's the best ROI/cash flow in real estate?

[Dan Stelter]

Hey everyone - 

I have a growing online e-commerce business. I've researched and understand the basics of real estate investing. I'm not going to switch any time soon. 

But as my other business grows, there may come a time where it makes sense to diversify income streams. If I want to make the best ROI on my cash, where would I start?

FYI, I live outside of Milwaukee, WI so not too far from Chicago.