I can't tell you what the "best" way to invest would be, but I can tell you the way I would most likely proceed.
I would focus on out of state properties for a long term investment. I would take that $150k and put it towards down payments using lenders local to the area you intend to invest. That $150k (assuming you use all of it and don't hold some back for early repairs/rehab) could get you $750k in property. Provided this is all self serving debt you could have $750k worth of property in 15 years once the notes are paid (assuming there is no market appreciation), and that's not counting the monthly rental income beyond the debt service.
Specifically where I am located I could make roughly $2,110/month assuming slight vacancy. That's after principal/interest, paying a property manager, taxes/insurance (not including any maintenance). This is assuming you purchase about 11 (roughly $60k-$70k) properties and use some of the funds for closing costs.
If you were patient and selective you could potentially even increase the monthly income a bit.
Just my take, and it's fairly specific to my area.