I have always had straight 2 horse loads. I have always tied; usually with a panic snap. Now that said, when I moved to CO, I did accidentally forget to tie my mare (had gone to give her her treats, and we drove for 2 hours with her untied...never even knew until I went to unload her for a break...Lol! But as a general rule, especially in a small 2 horse, I prefer to tie, rather than take the risk of the horse trying to turn around, which could end very badly for the horse if they manage to get partically turned and get stuck. I am keeping my eyeballs on a stock trailer owned by a friend who is hauling our hay for us, and I would likely turn it into a 'two stall' type trailer, and use the front for my mare, and the back for my tack and what not. Or maybe I would convert it to a slant, which I like too. Overall though, I DO prefer to tie...but that's just because of the trailers I have had to use, and tying I think, is safest.
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."