if going 2 horse.. i'd avoid looking for a slant. go straight load. also.. look for a combination stock trailer. very similar to a single purpose horse trailer, but other neat options like a chute door, etc.
make sure you have a front area in the trailer and an escape door.. very usefull.
if your horses won't trailer in dark areas.. install lamps.
get horse stall mats on the deck.
backup bunji whatever external type of latch mechanism you have. many trailers have a dual latch system, like a sliding bar lock, and something that cams over to secure it. even with this.. I have seen a kicking horse jar a door loose.
lastly, if you have a swing out door, make sure each lane/loading gate has a chain across the back so that when you have one loaded, it doesn't try to unload while loading the next one..
i have found some 2 horse bumper trailers that have non removeable dividers.. I much prefer removeable dividers.