We have a three horse slant-load trailer, and I'd actually consider selling it if it weren't for the removable dividers and collapsible rear tack. There's just so many problems I have with it... Three of my horses are just too big for the stalls, and even the 14 hand mare gets claustrophobic. If the rear tack wasn't collapsible, Ruby and the two youngsters are the only ones that would actually fit, much less load through such a small opening, plus there'd be no room to load that last horse and get out of the way if it panicked.
On top of that, we've had Ruby fall down in the trailer (she normally travels rather well) and unable to get back up... the trailer shook at a stop and I went back to check, and she was getting kicked by the horse next to her! We were just lucky that she was the last horse... I have no idea how long it would've taken were she in the front or middle.
We also have two stock trailers, and have never had an issue with them.
At any rate, I'm just curious... what exactly is the draw to slant loads? The only positive I've found to mine is that it's enclosed and has a tack room in the front... both of which are options I've found on stock trailers as well.