Rule number one for any investor is what is the potential ROI (Return on Investment). As with any geographic location, not only does value vary from one block to the next, but also from one home to the next. The best starting point for investment purposes is to determine your goals for ROI and assess what your annual goal is for return purposes. This will give you a starting point. Next, you will want to have a local agent from each of the areas give you a brief market analysis as to rental market, rental trends, home value trending, etc....
Further, I would recommend you consider several areas. As an investor you never want to put all your "eggs in one basket" Acts of God, such as hurricanes, storms, etc. can have a devastating ecomonic effect that is often not taken into consideration.
Last but not least, a good rule of thumb for any area in determining rental potential is analyzing the surrounding corporate and industrial climate. For example, Tampa is a PRIME rental market because you have several large employer groups housed here (ie: CITIGROUP) as well as a major AFB (Airforce Base- MacDill) this draws a large military population for rental potential.
I hope all this information has been helpful to you. Please feel free to contact me at your convenience with any questions you may have, I am happy to be of assistance.