Gman says he likes steel/wood because the floor is less slippery, making it less likely that your cargo or you will fall off. Also consider that an all steel trailer could be welded by almost any shop if you needed a repair on the road. Aluminum welding is a more specialized task that not everyone can do.. I have looked at some used aluminum frame flats lately that had stress cracks near the wheels. They had been welded up, but still did not look good to me. That said, I see more combo or all- aluminum trailers in use around here than all steel. Of course, rust is not an issue with all aluminum, but it's a big issue with steel, lots of rusty used steel flats around. Bottom line, I would buy the type that I got the best buy on, provided it was in good shape. Just from looking, it appears to me that an aluminum trailer should have a good arch from front to back. Steel trailers seem to have less arch, just my observation.