We updated from a 40-year-old popup to our first TT this spring and went through the same confusion. We made a list of "must haves" and "must not haves" and then visited several camper shows and dealer lots to narrow down our choices.
Some of our "must haves" included:
Walk-around bed
Dual propane tanks (some small trailers only have one)
3-burner stove with oven
Lots of storage
We found it especially helpful to visit camper shows that featured several dealers and lots of different brands so you could compare them all in one location. Be sure to open drawers and cabinets, some are constructed better than others. Check out the bathroom, make sure there's room to close the door and sit down without banging your knees. Make sure you can live with the tub or shower, some of the smaller units don't even have tub surrounds. If the unit has slides, make sure you can still access the bathroom or kitchen with the slides in.
Collect brochures on all of the ones you like and then narrow down your search at home by researching all the features on the manufacturers' websites. We started researching about 2 years before we were ready to buy but are pleased with our purchase and feel we found the right TT for our needs.
Once you narrow down your choices, revisit your favorites. Spend some time in them. Sit at the table, lie down on the bed, make sure there's room for both of you (and the dogs!) to move around comfortably on a rainy day.
And yes.... we did end up going with MY first choice. :D My sister and her BF bought DH's first choice and he now admits he likes ours better...