First off, if budget and aesthetics allow, it is always nice to use copper gutters. Aluminum, the most popular gutter material, has a realistic life expectancy in the climate that you are in of 10 years. Copper, on the other hand, will last for the life of the home.
The greenest choice for us is always the one that does not need to be replaced!
We also have oak trees along the back of the house, so leaves and seed tags blow into the gutters. Any green home gutter and downspout ideas?
As far as the leaf and seed problem, we took an idea from a product called Rain Tube. This product can handle 100″ of rain per hour and keeps leaves and other debris from building up. You can also get the same results for a lot less money by using a perforated, flexible drain pipe that you can get at any Lowes, Home Depot or irrigation supply company, and putting it into your gutter. It will keep out the debris and save you from the buildup of debris which will clog your downspouts and overflow your gutters.