If you are looking at buying stock in Realty Income (O -0.56%), you should probably also be considering competitor W.P. Carey (WPC -0.53%). There are a number of reasons for this, from their net-lease business models to their dividends. Here's a look at some key differences and similarities between these two real estate investment trusts (REITs).How are Realty Income and W.P. Carey similar?To start, Realty Income and W.P. Carey do very (very!) similar things. They both own single-tenant properties leased us ...