save yourself the money you will waste buying a cheaper steel trailer and pay more for an all aluminum the first time, You still have to wash the floor out but they will look new for many many years. ALL STEEL TRAILERS RUST !!! I don't care what kinda super duper bs finish this that or other the makers claim THEY ALL RUST, and all rust quickly, that's what people are doing looking underneath seeing how bad they are rusted out. Horse urine is corrosive to steel. Lots of used rusted steel trailers out there as people try to pass their mistakes on to the next person.
Aluminums weigh a little less, last a lot longer, and hold their resale value. Bumper pulls are handy and a aluminum 2 horse can be pulled with most V8 powered SUV's. Or some of the larger 6 cylinder ones with the right towing equipment added. I have a 2 horse aluminum gooseneck with a tack room/ sleeping area up front and a rear swing out tack room. It weighs 3600 lbs which is just a little more than my older steel (that rusted) 2 horse bumper pull with a bend over back killing tack area, and no where to sleep.
Look at the height also, taller trailers creat more wind drag and can make a trailer feel heavier on the highway. Trailers tend to be regular 7", tall 7-6 or 8, or short 6-6" 7" is fine for 16 hand and under.
SO in a nutshell, aluminum, look at the weight compared to what tow vehicle you are using and don't buy more height than you need.