Boy is this opinion, but my feeling is that you will be ahead with the steel. Galvalume is just a trade name for a type of galvanized steel. I have 30 year old steel gutters and, other than putting some sealer in the bottom of one, they are still going strong.
Our kids house has aluminum gutters and the place where a valley drains is always a problem, particularly with a snow load. As snow, or rain from a real heavy downpour, builds up, the weight just tears the aluminum out of the holders. They are on the second replacement in that area and each replacement was braced and secured more than the last. I have the same general arrangement on our house (steel gutters) and have never had a problem.
I keep thinking of new gutters--and they will be steel.