Hilltop,
This is a topic that you will likely get a dozen different oppinions on, ATLEAST! Hard to say which is the right answer but I'll toss in my $0.02
About a year ago I was in the same boat as you I had a steel trailer that was about 18 years old, though it was in good shape and I had just repainted it the year before I knew that sooner rather than later it was going to start to rust through. I advertised my old steel trailer on Kijiji and had numerous calls and e-mails on it right away. I was lucky enough to sell it for about double what I had paid for it a few years prior and was out very little expense for it's use. I had repainted it and replaced the axle tubes on it to get rid of the old drop axles that were under it when I bought it.
So I suddenly needed a trailer!
I had been looking and "admiring" for a few years so I more or less knew what I wanted.
I wanted something that was high enough for my horses and large enough for a decent size show string plus all the tack.
I ended up buying a 24' Sooner from Moose Jaw Toyota, they had the trailer on the lot and gave me the best deal I could find in Western Canada. In fact with the exchange at the time there is no way I could have imported one from the states for even close to the cost.
I chose the Sooner over models like the Wilson, Merrit etc because I found it was more suited to show cattle and bette suited for my horse, flat floor versusthe ribbed cattle floor and 7' 3" tall versus 6'6" in the Wilson. Mine is 7' wide, I would love to have a 8' wide trailer but it is substantially more money and not worth it in my mind. I preffer the flat sides and the airgaps up high like the Sooner, Featherlite etc much easier to close in for cold Canadian winters. I got the removable plexiglass insersts and rubber mats in mine as well
I also found that the spread from used trailers to brand new ones was relatively small, so I chose to go new. Made more sense in my mind.
The other model that I asmired as well was the Sundowner, a VERY well built trailer in my mind.
I would call the guys in Moosejaw for a quote first, they were very easy to deal with.