I have owned more trailers than I care to admit to- everything from a two horse straight load bumper pull to large 4 horse slants with living quarters, probably more than 10 in total.
The one I will never sell, until we are totally out of horses and livestock, is our stock trailer.
Gooseneck, 16’ on the floor, 6’9” wide, calf gate into the neck, full escape door in the front compartment, center full swinging gate with a sliding door in it, and the same full gate with a sliding door on the rear. It is only 7’ high, but I have short, cattle bred QHs and Paints, so it works for me.
The only thing that would make me love it more is if it had a real dressing room/ tack room up front, and a ramp either at the rear or on the side.
With the center gate, it makes 2 8’ long box stalls. Great space for 1 or 2 horses per box, depending on the horses.
I have loaded a feral horse on it more than once, as well as horses that hadn’t been hauled for years and problem loaders.
One of the things I like about it best is it is safe for both horses and those loading the horses. There are plenty of places for a human to get away from a fractious horse, and you can even open the center gate from outside the trailer.
Ours is all aluminum, and I bought it in 2011 for a mere $6500. It is a 1999 that is hard to tell its age as it has held up so well. We just replaced the mats in it last year, make sure all the hinges and latches get lubed regularly, and replaced all the lights with LED lights a couple years ago. Other than brakes and tires, there is not much to it.