For my Massey GC2600, which I figured I might trailer a few times a year, I was in the same predicament. Single or double axle, aluminum or steel. Steel was quickly ruled out, I've yet seen one after a few years which didn't look like a bucket of rust. I ended up with all all aluminum landscape/utility 6x12 (aluminum floor as well) with a single 3,000 pound axle. The trailer tare is only 600 pounds so can carry about the same as a 3500# axle steel trailer and much easier to move around the yard by hand if need be (the same size steel trailer weighs in at around 1100#'s). I worried a little about the floor getting banged up with rocks but think I'll get a rubber mat for it which will help with that.
13*My tractor with loader weighs around 2100#, on the trailer the tires are barely deflecting and it tows excellent plus there's room for more weight such as my boxblade or mower deck.