Another thing to consider is if you live in a part of the country that's prone to ice and snow, aluminium may be the better way to go.
I live in SE PA and on average we get 26" of snow per year. We have drastic changes in temperature during the winter season where it will rain during the day and snow and freeze at nite. This may put a little more stress on vinyl gutters over time than you'd care to live with. IMO, if you live in SC or south, vinyl should be just fine!