The trailer I have is a straight load but has no tack room at the front so its wide open. It was also as tall and wide as they come so it was huge for anything less than 16'2-3 hh.
If you are looking at a trailer I would strongly encourage getting a straight load, especially if you arent sure of what kind of horse you will have in the future. By getting a second good sized straight load you will have that peace of mind of knowing you wont have trailer issues.
An old friend of mine bought a straight load but its minuscule. She owns 2 warmbloods (that are tiny by the way) and now just traded one of her horses for a 17'2 hh mutt and she is now trapped with a trailer (she just got) that she can't use.