You can do well, or poorly, in either area, since the local markets vary within their boundaries.
I know that rentals are in demand in Cary/Morrisville, and expect as much in Durham.
Rental rates tend to be in the range of .6%--.7% of the home's sales value.
I.e., a $225,000 home may rent in the $1350--$1500 range.
Going for a higher return may be possible, but also increases the risk of non-payment and vacancies. Other than tenant damage to premises, vacancy is the #1 cost factor that destroys cash flow for landlords.
I would look in Cary and Morrisville as a desirable area, for proximity to good schools and easy access to RTP.
I own rental properties in Durham, Chapel Hill and Carrboro. If I were buying now, between these 3 locations I would buy in Durham. Morrisville, Brier Creek, Cary, are all very popular though Durham is the hot city right now. It is best to look at rental properties as a long-term investment strategy because it isn't easy to get a quick return. One of the other things I do and advise is to improve the property so that you create more equity and higher rents.
I'm always happy to discuss this because I love real estate investment. I've made mistakes, done well, and a whole range in between.
Vivian, aka CrazyViv