So, growing up in the car business and now married to a manager of a large dealership, here's my 2 cents.
I'm not going to tell you which brand to get, that is going to be up to you, but I think it more important to find a truck that can do the job for you other than which badge it has on the grill.
ABSOLETULEY WITHOUT A DOUBT I DON'T CARE WHAT ANYONE ELSE WILL TELL YOU GET ONE WITH A FACTORY TOW PACKAGE!!!!!!!!!!!!!!!!!!! One that just has the correct sized hitch on the back isn't good enough. The factory packages have extra stuff under the hood like extra cooling and such to keep truck happy and not burn it out(oil and tranny). Also most have a heavier braking system and suspension and the wiring for your brake box(different brands have different stuff standard), but all factory packages have the stuff you need to make your truck last longer.
I would strongly recommend a 4x4 as well, or at the very least something with limited slip. I am in FL, so I don't have weather issues that need the 4x4, but I would never have a truck without it. heavier suspension on a 4x4, plus I have seen people get stuck in loose sand here. If you do have snow, then no question a 4x4. This will also give you a higher payload in your bed if you are using it as a farm truck too and may need to put loads of dirt or clay, or round bales, or whatever in your bed.
Also strongly urge you to get 4 wheel disc brakes, NO DRUMS!!! Although this seems to be standard on most trucks now, I don't know what you will be looking at or how old it may be. People like to forget that the truck has to be able to STOP the trailer easily as well( yes, i know you will have brakes on your trailer too). hope this helps!
Whatever brand floats your boat. I have a 10 yr old GMC 3/4 ton which I love.
1) Factory Towing Package only
3) Minimum size 3/4 ton. Don't get a 1/2 ton, even if you think you are only hauling a little and one horse. Killing the truck and starting over is a lot more expensive than buying enough truck the first time around.
If it's used, always have a good mechanic have a look-see! Don't buy something which has had a plow on the front, either. That's asking for issues down the road.
Brand is like religion, LOL. But as for a tow package, you want a factory tow package. Don't settle on that one. I actually traded in my 4x4 and don't want it, but I do not live in an area with much snow. I find it increases maintenance costs and reduces mileage and I almost never used it. Not worth it for me. If you are hauling once a week, go 3/4 ton. That's a lot of work for a truck!
This will not be my primary vehicle and I won't be trailering to shows. I'll probably be trailering 1x per week max 1.5 hours one way. That is the longest that I'd be going.
I want used and not too expensive. I will only be hauling one horse at a time.
Otherwise the truck will be used as a farm vehicle...drag the ring, pick up hay/feed etc.
Suggestions? And do I want one with a tow package already?
It depends on how old! All of them had bad years during certain periods/better in others with engine changes etc. I would not touch one of the early Rams with the new engines but the newer ones the problems are fixed. I love my 99 FOrd but would not buy a new one now. If I was buying a newer one I would go Chevy with the improvements they have made. Clear as mud??