The weight savings on an all aluminum trailer versus a steel trailer is 20% maximum. Due to the fact they have to use more aluminum to maintain structural integrity. So on a 10,000 pund trailer you knock off 2000 pounds to say 8000 pounds. Not much there just for weight, but the rust factor will be brought up by somebody shortly, then someone will try their hand at aluminum/steel trailers electrolysis causing degradation and rust using two dissimilar metals in conjunction with one another (this is semi-mythical scenario), next you'll hear about the fact that though aluminum doesn't rust, it oxidizes, and last but not least you will learn there is NO such thing as an ALL aluminum trailer, as the gooseneck coupler and frame will indeed be made of steel.

All that said, all 3 trailer construction options offer good points and nice trailers, but no matter which one you get if you don't take care of it, it will deteriorate. It's all about personal choice, get what you like, from a reputable manufacturer.

I modified my post after realizing my amazing mathmatical skills were skewed in my original post as noted below.

The 20% number might be a bit high but in any case, 20% savings off 10000 lbs makes it 8000 lbs, not 9800, which is a pretty significant decrease.