Ooh, hit a raw nerve on this... Could go on for pages and pages but won't. At the worst, some TTs can end up being a problem from day one and costing you a ton of $$, aggravation and lost sleep not to mention ruining camping outings. It's a really good idea to be investigating before paying for a new unit, then finding out stuff.
If we were to be looking for a new TT, I'd be looking closely at a Nash, Arctic Fox or Outdoors RV (all owned by same co.) - not being built in Indiana and not having a Lippert frame would be a major plus to me. Maybe Lance as well. Not to say these don't have issues, but are far ahead of most others IMO.
So many problems with TTs in general, ranging from not serious to extremely serious... Little to no quality control and no industry regulations that manufacturers must follow. We're on our 3rd TT in about 3 1/2 years and I could never have possibly imagined the problems we'd run into until owning one. Anything designated ultralite can potentially have more problems because they build them the lightest they can with the thinnest, lightest and least substantial materials and cut corners all in the name of saving a few lbs. Forget about making a buying decision based on dry weights as they mean nothing in the end. Some TTs have a lot of available CCC and some have nothing left when you've loaded them up with ordinary camping gear and supplies (ours has only around 200 lbs left with empty tanks and towing with just one full tank would put it over the GVWR).
If you come up with a short list, I'd look very closely at the construction details, methods and workmanship throughout. Pull cabinet drawers out, look inside upper and lower cabinets, inside dinette seating etc. and see how good the construction is - do cab. doors and drawers open/close smoothly and properly; are things fairly plumb, level square and straight; etc., etc. Look underneath and inspect the frame - some have very good frames, most have decent ones, but some are not good at all and some frames have better re-enforcing than others. Does the subfloor flex a lot when you stand still and someone walks around on it? Lots of things you can inspect. If you are serious about finding something good, I would find a good independent RV repair shop who has someone who will talk you about different brands and things to look for, even if you have to pay for their time.
Friends of ours have a Keystone Cougar 1.5 yrs. old and I just spent a whole day fixing up the crappy cabinetry that was falling apart. Absolutely the worst cabinetry workmanship and quality I've seen in a TT. If they had the money, they'd get rid of it. A lot of TTs look great on a dealer's lot or at a show, but it's what's not immediately obvious or lurking beneath the surface that can get you.
Anyway, choose wisely and enjoy your TT!