That is like asking me what type girls/ guys you should date!!!!
What type rentals are you interested in? What is the market for that type in your area? What is the overall housing market in your area of interest? What are the most significant economic drivers in your market and how will they be changing in the next year, 5 years 10 years. What is your experience level in Property Management? Are you licensed and are you a qualified Property Manager? What is your financial goal and status? Do you have a basic plan or idea about any specific area/ type of rental property?
Working with rentals is actually not good or bad. While I personally think Property Management sucks and is a clerical job, it is small part of my brokerage activity that I reluctantly oversee, it would never be one I would care to be involved with full time... I hire clerks to do it for me.
As far as pure investment with out the day to day Property Management operations, it is a far more attractive element of interest to most investors. You still have to determine what type and how your personal capabilities would fit that specific type investment.
All investing is a mathematical problem, rentals are a marginally more complex math problem but one you must be able to use to make sure you are an investor and not just a speculator or simply a gambler or worst.