A three-season tent covers spring to autumn: rain, wind and the odd cold night, but not heavy snow. Start with the number of sleepers and add one if you want your pack inside. Two doors and two vestibules sound like a luxury until you need to get out at night without climbing over your partner.
Look at weight and packed size next. A two-person tent around 2.4 kg is a good compromise; going lighter usually costs durability. Check the waterproof rating of the fly (1500 mm is enough for the floor, 3000 mm for the fly) and make sure the seams are taped.
Finally, pitch it at home before the trip. Ten minutes in the garden saves an hour in the dark.
