An open trailer does have some advantages. I towed my Cobra around on one for quite a while. Didn't get any damage that I could see. Low wind resistance, easy to tow. Made by Parker. Very solid and well balanced trailer. I would recommend it to anyone.
All steel is usually better, IMO. They usually last longer and need less maint. Wood decks need to be rplaced periodically. But they are a bit heavy. Depending on your tow vehicle, that could matter. Open center trailers like JDog's are a bit lighter, and you can work under them. But it limits use a a little bit. Hard to put a load of lumber or sheetrock on it.
Alum is nice. But have you seen the cost of an alum trailer lately? Holy cow. It costs you 40% more $, and saves only 20% of the weight.
I just bought a Serpent Express last month. Havn't had the Cobra in it yet, but I towed it home from UT. It's very nice. More $$ than a simple flat bed, but a whole lot less than an enclosed. Weighs less than my flatbed, too.