Consider your priorities relative to how you will use the tent: Weight, Size, Security of Performance, Convenience, Features, Cost. Gaining advantage in one area always comes at a cost in another.
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WEIGHT. Less is always better? +
Unless someone else carries your tent, a lighter backpacking tent has to reside fairly high on your list of priorities. Fifteen years ago anything under 6 pounds was light. Big Agnes led the market all the way down to around 2 pounds. But to get there you have to spend a lot and give up a lot in features and durability. Even today, 6 pounds is still about the number if you want a roomy, durable, easy-to-pitch, low-cost tent.
SIZE. Bigger is better? +
Not unlike a car buying choice, bigger offers a lot of what most people want. Of course bigger comes at a weight cost. An ounce counter leans toward smaller, recognizing the body pays a price for every one of those ounces packed on the back. Think about the amount of space you actually need to be satisfied vs. the importance of gaining or losing a pound or two in what you have to carry. Bigger may be better for camping. Lighter is always better for hiking.
SECURITY OF PERFORMANCE. What is your risk level? +
For most of our early years we relied on cheap tents. We had no money, and any shelter at all was better than the none we were used to. We didn't (plan to) camp in difficult conditions or more than a few days and were rarely more than a few hours from the car. Cheap tents offer a lot of camping comfort, and because they typically have minimal flys and polyethlene bottoms, they can be on the lighter side of average. Now we expect to be out in whatever Nature may offer, and we want the security of knowing our gear will be up to the task. We would be gravely disappointed with a gear failure early in a week's trip; or from an unexpectedly severe passage of weather. The ultra-light sil-nylon versions tempt us for the weight, but leave us wondering if they will deliver the durability we expect from spending so much money. On the other hand, we typically aren't exposing ourselves to life-threatening conditions. We don't often need tank, and generally don't prefer tissue. For each trip, we ask: "What happens if this piece of gear fails?"
3 or 4 SEASON? 1 tent for all? +
We camp every month of the year, frequently in the High Sierras of California. Of our personal stash of 20+ backpacking tents, 2 are 4-season and neither gets much use. Most summer campers don't need 4-season and won't be as happy. 4-seasons have more pole structure and typically much less netting area (usually with a zip cover). They tolerate sustained high loads from wind and snow. They are generally heavier. They usually don't have as much ventilation, and can be unbearably hot in sunny temps. When your survival in harsh conditions depends on your tent, choose a 4-season. Otherwise, save weight, money and enjoy your adventure more in a 3-season tent. We are not aware of a single design that satisfactorily services all-season camping.
CONVENIENCE. Faster pitching is always better? +
In the dark, in the rain, in a stupor of fatigue, having to solve riddles in pitching the tent can be no fun. Free-standing tents are much easier to pitch; and if you don't like where it is, simply pick it up and move it before you peg in the fly. Poles add strength against wind and snow load. Poles add weight, typically about a pound. A key tactic in losing tent weight is engineering less pole structure. That also means less structural integrity, less interior volume, more fiddling to peg the tent down to pitch it and more guy lines surrounding the tent.
The choice is one or two. Two is always better, and we always prefer on the side. Of course a second door adds weight, production cost and another zipper to fail. We gladly accept those costs in favor of comfort. We're only out there to enjoy the experience. Side doors are simply easier ingress and egress, and the less young we get, the more we like them. With two people, each needs a door. With one person, the second door makes convenient access to the pack stored under the largest area of vestibule. With two doors it doesn't matter which side the door is on when you pitch the tent.
POLES? Not much choice here. +
If you want a free standing tent, you haven't much choice but poles. A cheap tent will have fiberglass poles. They tend to be heavier and will ultimately fail from radial fractures. (We amuse ourselves with ever-increasing amounts of packaging tape to keep our venerable cheap tent poles in one piece.) Premium tents generally use aluminum poles for lightweight strength and durability. A few might have carbon fiber or some exotic alloy. The weight savings vs. cost can be a point to ponder; and in the case of carbon fiber, they don't hold up so well to UV radiation. Shock-corded means the pole sections are held together with an elastic cord running inside the pole. Someone once gave me a tent that did not have shock-cord, and I quickly in turn gave it away.
FABRICS. All cut from the same cloth? +
A cheap tent will almost certainly have nylon taffeta walls and fly, perhaps with a bit of ripstop in sensitive areas; and polyethlene floor. Ripstop is usually the choice for premium tent walls and sometimes the fly. Floors will most often be taffeta. The fly is likely to be polyester taffeta. Ultra-lights use more ripstop, though in much lighter denier (thread diameter); and rain-exposed fabric will most often be impregnated with silicon for strength and water resistance. Polyethene is light and waterproof, but the coating tends to break down in creases and the material has little puncture resistance. Taffeta hasn't the tear resistance of ripstop, but the smoother surface takes coating more evenly with less chance of defect. Ripstop is stronger. Nylon is stronger than polyester, but polyester doesn't sag as much when wet. If any part of the tent is likely to get wet, it is of course the fly. Taffeta is more likely to have a perfect application of coating, and polyester won't stretch as much when wet.
ZIPPERS. Really? +
Zipper failure dooms most tents to the waste bin. A cheap tent costs less than the zippers in a premium tent; and when the zipper fails, no big loss--unless you spend the rest of your trip exposed to weather or bugs. Most premium tents use YKK brand. Ultralights shave weight--and sacrifice durability--using a smaller size. Tents have to withstand a remarkable amount of abuse, and at the forefront of that torture is your zippers. Paying more does not guarantee you will never have a zipper failure; it only reduces the risk. So once again, the question is what level of risk makes sense for the way you want to use your tent; and what happens if the zipper fails?
POCKETS? Most people look for pockets, and indeed +
they can offer convenient storage and ready access. We wouldn't let pockets move us one way or the other.
ATTIC? An attic puts handy storage right above your head, +
but then, it's right above your head. Most backpacking tents are small enough that reducing peak height even for a laudable purpose seems hardly worthwhile.
PEAK LOOP? If you've ever wanted light in your tent +
then you know a peak loop is about the only way to suspend it. We rarely use it, but it can be nice to have.
FOOTPRINT? How long do you want your tent to last? +
We just don't sleep well fussing over the abuse to the tent floor without a footprint. Yes, it is a high margin item and tent vendors love to sell it. But they'd actually make more money selling you another tent sooner. Use a footprint to make your tent last longer. Shiny side up, and of course underneath, not inside, the tent.
TAPED SEAMS? The old and tested alternative +
is seam sealing, which works fine but requires a lot of patience. Most premium tents are seam-taped at the factory. Only coated-fabric seams will be taped.

90-second version How To Choose A Backpacking Tent: