Start by searching here.... http://www.horsetrailerworld.com/home/searchtrailers.asp

You have lots and lots of choices.  Your best bet is to set a budget and determine what your towing capacity is, then narrow your search from there.  

Are there specific features that are must-haves for you, such as slant load vs straight load, or extra-tall or extra-wide for big horses?   If you share you must-have and wish list, others who have shopped for similar trailers could help you in the selection process.  

What is popular and available in your part of the country will have a big effect on your choice as well.  The brands we see out west are not the same brands you probably see in the midwest.  So keep in mind recommendations are many times regional. 

Since you will have many choices, do as suggested as figure out what you must have, want to have and maybe thinging of having. Look at other set ups at dealers and from friends.They can be far more open about what features have worked out the best for them.

You needs will also play a big part. Are you just hauling occasional rides or is this going to be something you need weekly? I'd want a large dressing room with a rear tack.I don't have a preference for ramps or managers, they both have pros and cons. I'd say just about any major brand of trailer is going to be safe but some might have a few extras that make it a better buy such as insulation in horse area.

Your budget plays a big part- if the sky is the limit, then buy whatever suits you. If not, then you will have to pick and choose the trailer that meets most of your wants. I'd be looking at Sundowners,Exiss,4Stars and featherlites. There are so many out there but these are the ones I see on the road so you'd think people are drawn to them for a reason.