Everything depends on the property. I would say out of all of the areas here, the ones that are easiest to rent are Cambridge, Newton, and Jamaica Plain. Belmont gets a bit of traffic, as well as Needham and Watertown. Cambridge and Newton are probably your two best options though if you're looking to invest. Cambridge has really low property taxes, and that attracts a lot of investors.
I would be happy to assist you with your search further. Please contact me at 781-330-0152