If you plan to contiune buying Rosa' then I would probably buy the Martin book (Probably more in depth detail on the series). If you just have a general interest in the Colonials then I would go for the Whitman book. Not as detailed but t covers a much wider range and allows for the attribution of many series of colonials. If attribution is what you really want the Whitman book replaces several specialized books. If you start getting serious in any of the different series then I would recommend going ahead and buying the standard reference.