My Mantra has always been, rent before you buy. 
Even though you try to check out the items above, chances are you will buy the one with the floor plan you like. Regardless of the other feature suggested, a bad floor plan comes back to haunt you continuously. 
We rented a TT with the floor plan we had to have and after 10 days, it was not what we wanted. We searched for a used model with the layout the DW wanted and found a three year old unit that has served us well for 25,000 mile over the last three years. 
Three other things that come as a shock to many new TT owners.
*  You will get 10 mpg.
*  You will find 300 mils a day about average.
*  Your average speed will be about 52 mph. or a 250 mile trip will take about 5 hrs.
*  You will be passed by everything on the road, because nobody like to follow a TT. 
Again, when you rent one of these barns and pull it down the road, you learn a lot very quickly.
RV travel is unique and can be a lot of fun.
Good luck,