Q. The 20-year-old galvanized gutters on my house are worn out. Would you suggest I replace them with aluminum? A. If we assume that the configuration is the same, galvanized gutters usually cost more than aluminum, bearing in mind that the aluminum is lighter gauge.
Increasing the cost of galvanized gutters is the initial need to apply two or three coats of paint, plus periodic repainting thereafter. Aluminum needs no paint if it is aesthetically acceptable in its natural color.
The lighter-weight aluminum is simpler to install.
Which metal will last longer? Assuming both metals are properly installed and maintained, rustless aluminum has greater longevity from water contact.
So why don't you put together the pluses and minuses of both materials and make up your own mind as to which to use? Both will satisfactorily carry away rainwater for 20 years or more.