Depends. For us, the main things we want in a 2-person tent are interior volume and light weight. Also important are two doors on the long sides (easier to get in and out), and good vestibules. We don't care about single vs double wall, or freestanding.
The three commonly recommended 2-person tents are the Tarptent Double Rainbow, the Lightheart Gear Duo, and the Six Moons Designs Lunar Duo. Lately the Zpacks Duplex and Triplex can be added to the list. (
See here for a photo comparison of the first three.)
We've owned three of these tents. The best, for us, were the Lunar Duo, which is just simply the best interior volume of any 2-person tent we've ever seen, and the Triplex, which is similar in design but over a pound lighter. The Lunar Duo is a bit tricky to set up, but it's easy to use the doors, has two great vestibules for gear, and the interior room is just amazing. The Zpacks Triplex is wider, with similar headroom, and easier to set up, but the doors are a PITA to open and close. (The Duplex is just a narrower version of the Triplex, easier to fit in small tentsites but less room for gear and people.) The Lunar duo is less than half the price of the Triplex and gets my vote as the best buy for a hiking couple. The Lunar Duo kept us dry and happy in some serious thunderstorms over the years -- we finally passed it on to a friend and got the Triplex to save the extra weight, but I will miss it.