The floor plan IS the most important thing!!
If you are looking at new campers, all units of a similar size and similar price will be very similar build quality with nearly identical quality parts. Virtually all TT manufacturers use one of the two brands of RV refrigerators. Same for water heaters, stoves and furnaces.
Why buy new? A gently used 2 or 3 year old unit can save you thousands of dollars. If you decide camping is not for you or if you love and want a bigger camper, you lose much less money when you sell or trade.
Almost all campers, especially entry level ones, have numerous flaws from the manufacturer, requiring several trips back to the dealer for warranty repairs. Some dealers are very slow getting to low reimbursement warranty jobs, so your camper may sit there for a month or more. You must still make payments, but you can not use the camper. A gently used camper will have most of these things fixed, so you can enjoy using your new toy.
What is your tow vehicle? Not every SUV can pull every TT, despite what the dealer tells you! You must be better educated on tow capacities than the sales staff. Fortunately, that is pretty easy to do, and you are at the right place to learn!
http://www.rvforum.net/SMF_forum/index.php/topic,90933.0.html
Enjoy the search!!