Not sure what your going to use it for exactly, but I'd avoid the witzco trailers, make sure you get a non ground bearing trailer if you go detach, yes others are cheaper and lighter, but if you need to detach in the dirt, mud, on gravel roads, anywhere off the beaten path, you'll like the non ground bearing feature. I personally wouldn't ever buy a ground bearing trailer but I run in adverse conditions off the beaten path. Yes trailers are high priced, not sure why used is out this world right now, condition makes a big difference, new has gone up so much in the last few years because of steel prices, used has followed suit I guess, like everything else.
I run talbert and rodgers trailers myself, I like them both, I'd stay to a major manufacturer, not those that cater to the auction sales sites. There are a lot of great trailers out there, as for one being better than another, yes, but there are still a lot of good quality trailers out there made you can afford. As for witzco trailers I've seen a few with the side rails blown out and the deck laying on the ground, wasn't real impressed myself, also look at the load capabilty of the trailer in the span length, this is very important for a lowboy, it doesn't do any good to be able to carry 35 ton if you have it have it spead out over the full length of the entire deck say instead of in 10-15 ft length like most tracks are long on machines. Thats the biggest difference in trailers, also the big name manufacurers make different quality trailers, my rodgers is a cheaper version of the 50 ton triple axle trailer, it works just fine but I don't load it full and run everyday over the road either, but its still far better than any witzco trailer.
As for the pony motor verses wet kit debate, I've got both, I absolutely hate the pony motor trailer, why, because when you need it it won't start, you either drove in rain, cold, snow or its out of gas or the battery is dead, anyone can brag all they want about saving weight and expense of the wet kit, but for me once the truck is running I have hydraulics and can run the trailer as well, will they both work, yes, but after years of use, I've spent more money on upkeep on the stupid pony motor than I ever did on the wet kit. Also look to see where the pony motor is mounted, some rocket scientist years back decided it was a good idea to mont the motor in the belly, great idea, saves space, just once the trailer is loaded, you can't access the motor if it won't start, same goes for mounting it in the neck, had it a few times where I had stuff backed up the neck and I couldn't get at the motor, mount it on top of the neck and you are standing on top of the neck to pull start it after the battery is dead in the rain and snow, fell off mine a few times doing that as well. I've had mine mounted on top of the neck, in the neck, both were a pain in the a**, on top it was too high to reach, in the neck you had to pull the motor out every time there was a battery connection problem on the starter, like it has right now, so we pull start it every time, also road salt and dust raises havoc on the connections for the battery no matter where its mounted on the trailer. I just haven't had time to throw the pony motor away and mount up another two line wet kit on my second truck yet, one of these days, when its probably snowing or for some reason the pony motor won't start I'll take it off and throw it away and pull the truck into the shop and bite the bullet and just do the twon line wet kit on that truck too.
As for my trailers, I run dayton wheels yet, probably wouldn't recommend that for most, I'd probably go bud style with outboard brakes and 22.5 tires, mine are super low pro 22.5's and are hard to find around me so I keep several spares on hand, if possible go with a tail and ramps out the back as well as the detach, wish mine had this feature
Go with the longest bed length you can, my 35 ton is only a 20 ft deck my 50 ton has a 24 ft deck, wish the 35 ton had the 24 ft and my 50 ton had a 25 or 26 ft deck. The shorter decks are limiting what you can haul, for example I've got several machines I could haul on my 35 ton trailer together but they won't fit on the deck at the same time, weight isn't a problem its the deck length, same for the 50 ton trailer, now in my state I can legally haul up to 86,000 on 6 axles but two machines won't fit on the deck length, if it were longer I could do that. Just a few ideas to toss out there for you to ponder over, best of luck on your search for a trailer.