The type of property you want to wholesale is existing single family homes, duplexes or triplexes, that are deeded. Apartments are too complicated to deal with due to the associations, and you do not want to wholesale a commercial property.
Non-deeded properties will depreciate over time.
In our experience there are always more buyers in the middle price range, so make sure to target middle class family homes, in a decent neighborhood; an investor will not buy a property, even if it's a great deal, in a bad neighborhood or if the home is near businesses or any commercial property.