Help assessing the value of my rental properties for the purpose of selling

[William Allen Ball]

I have a portfolio of 9 doors (2 duplex, 5 single family) in Northwest Arkansas.  I am looking to sell all to one investor, if possible.  I have only ever bought, so this is my first time to sell.  I am trying to figure out the best approach to price the portfolio..  Income approach?  Gross Rent Multiplier ?  Sales comparison ?  These properties are in desirable parts of Bentonville and Bella Vista AR, with no deferred maintenance, but several units are well below market rents with long term tenants.