I've had a lot of experience with trailers, mostly 5th wheels though. A few things I can tell you is that most likely you are going to have at least a few problems even with brand new ones no matter the maker. I work closely with an RV repair facility and the owner says that the quality control from the factory is crap and the pre check by dealers is lacking. This mirrors what I have personally seen. He says that dealing with anything Forest River for warranty is a headache and Keystone is pretty good on warranty. Also, there is such a large profit margin written into what the dealers make that they able to cover the warranty problems that will inevitably arise. If at all possible buy a trailer from a local dealer that you can go back to for warranty issues. All dealers will tell you that you can take it to any dealer or warranty repair facility to have it repaired but that is an out right lie. Most dealers won't do work on something they haven't sold even though they are supposed to. At best, you will go to the back of the line. This is because the company pays so little and makes dealers jump through so many hoops on that they are losing money on warranty work.
I wouldn't be afraid of a used trailer although I would want a very good history, preferably from someone I trust. What its been used for, if its been stored inside, etc. Used trailers have usually had issues worked out and often have some cool, and expensive additions. If there is any sign of water leaks, and I mean any, walk away. Water leaks are trailer killers, especially around the roof line.
On new and especially used, check everything. Get up on the roof and see look for soft spots, seals cracking and sun damage. Check all appliances, heaters, a/c, etc. Look underneath and see if the under liner has ever been cut or opened up. NEVER trust a dealer who says they have inspected everything.
Last, weather kills trailers. Sitting outside in the sun and rain will cut the life (and looks) in half. Good luck and understand that trailers are poorly built and are basically going through a 5.0 earthquake every time you tow them.