your rate of return will reflect the "risk" you are willing to take
the riskier the investment, the greater the return.
historically, it has been "best" to invest in the stock market.
the best way to invest in the stock market is to have a diverse portfolio of stock (25-30) that cover a wide range of
businesses, or
invest in a index fund (mutual fund that does that for you)
over the "long haul" (typically 10-20 years) rate of return will be roughly 10-12% (using historical facts)
short term fluctuations wil occur
taxes and such need to be factored in
the idea is that you can't really expect reasonably to make a rate of return greater than that which is the average o the entire U.S. economy - hence the stock market.
by the way - don't forget insurance for your house...
the odd tenant that will trash the place and run off..
also don't forget potential appreciation of the house if you sell it, and the advantage of a mortgage with the tax writeoff of the interest (as well as your "operating" expenses"
probably, if you have a separate income, and other investments..diversifying is wise, and rental property is one way to accomplish this.
if your short on time, not the handyman type, and don't like dealing with crabby tenants-- easiest way to invest (over the LONG haul) is still a index mutual fund.
good luck. hope you do well.