As you bring on more units and you have a more diverse tenant base, not meaning race, but age, you will find that older people generally prefer to pay one way and the youngsters another and the large group in the middle will be pretty uniform. 

I am excited, humbled and favored to be in this wonderful platform of great, successful people of humble beginnings, from diverse backgrounds.

Fannie Mae & Freddie Mac are promoters of home ownership and  though they will finance up to 10 residential properties for an investor they WILL NOT finance LLCs.

I have been a stalwart promoter of BP's podcasts, books, forums, and in-person events.

He's promoting a direct mail service for investors and mentiones a 10% response rate.

Diversity of all. 

The population has been growing here year over year over the last decade, it is home to The Ohio State University which has over 50,000 students that live here along with those that visit, and it also holds a diverse range of young professionals and traveling nurses to fill the demand of the multiple business corporations and hospitals stationed here.

You will find others who promote a 1% strategy (if home costs $150K then must rent for $1500/mo), but my strategy is based on return and risk.  

Sorry Simon, bit of confusion as the moderators thought I was promoting myself.

I would bet on cities with decent past and projected job growth. if the economy enters a correction, people will stay/flock to cities where there's jobs. there were some good cities already listed above but you'll also want to check that there's a diversity of economies, that it fits within what you have saved capital wise and have some local investors/connections already there who can help you out with building your team.