I would agree w/Henry's line of thinking ESPECIALLY where it comes to heavy 'loads'. If you happen to live in a climate such as I do in the Mid-Atlantic states, aluminum gutters are fine. Down south, where it doesn't snow (or it snows a very little on rare occassions), folks have plastic gutters.
IF you decide to go EITHER type of gutter, I recommend you go w/seamless gutters and hidden hangers. This way, there are no 'sections' that can leak. Galvanized Seamless Gutters and Aluminum Seamless Gutters (see examples) are made custom, on site. And, there are enough colors to choose from.