Bed. Many people don't like drop down dinettes, but our U-shaped dinette drops down to make a huge queen sized bed (almost queen size, but close enough!).
Simply adding a 2" memory foam topper makes it extremely comfortable.
We've had essentially no problems with our TT. This will be its 12th year of camping, and it is starting to show its age. We are hoping (and assuming) it will last 2 more seasons, then we will probably be looking for something new.
Our truck has just worked. Up and down the east coast twice and all over New England. I wish the seats were a bit more comfortable, but they are supportive and fine for long trips. I just had the transmission checked and fluid changed, and had the spark plugs replaced (this is the 5.4, with the legendarily horrible spark plug changing issues, so I had a trusted repair garage do it), so I am expecting to keep this truck for a bunch more years. Next spring I am planning on having some body work done on it for rust prevention - well underneath the bed, out of sight, where the bed bolts to the frame. Essentially no rust on the truck except for that one area.