Double check your car before having a tow bar fitted, not all 4x4s are big enough to tow horses. Check the braked tow capacity, you’ll need 2t minimum and really that only lets you tow 1 horse because you have to take in the weight of the trailer too, even if it’s a 2 horse trailer it doesn’t mean your car is up to towing 2, it’s generally not if your car can pull it, it’s if your car has enough weight to stop it in an emergency without the trailer coming sailing past you because it’s heavier than the car.
Similarly with 3.5t check the weights, if the van itself is 2.8t that only leaves 0.7t available for horse, tack, driver, fuel, hay etc. as if you go over 3.5t total you are illegal. There are many out there stalled for 2x 15.2 horses which in no way have the weight capacity to carry 2!
As for preference, I’d love to have a 3.5t just to be able to Have stuff already packed and jump in and go but I’ve not been that lucky and have always had trailers and it’s not that much extra bother, I used to regularly go out schooling a couple of times a week and hack or show most weekends, you just get better at packing and hitching up ?