As others have said, depends on intended usage.
"Expedition" tent, "4-season tent", and "4-season mountaineering" tents can all have different meanings and different usages. What is your intended use?
For "expedition" your main focus is strength, square footage, liveability (which includes fq ft but also things like doors, windows, vestibules, top height). Definitely want a 3p size for 2p, because you will be spending a lot of time in it. It's probably going to be big, heavy, and expensive. Likely double wall.
For "4-season", ie backpacking and snowshoeing, you want those same things, but can sacrifice strength for weight (doesn't need to withstand Himalayan winds, just a good winter storm, hopefully nestled in the trees or off a ridge). If you're planning your trip and not stuck on a glacier, you probably won't head out into a blizzard, right? And you can get cheaper, quality options. REI and Kelty make some 4-season tents that are quite good for winter camping.
For "4-season mountaineering", weight and necessary (not comfy, necessary) sq ft are the drivers. You also want fast setup, particularly in the wind. I like singlewall for that, although there are some innovative double-wall tents with the fly permanently attached. I don't own one, though.
My choice: http://www.sierradesigns.com/p-148-convert-3.aspx
. It wouldn't be my first choice for a long expedition, but since I haven't been on a long expedition I don't need those features. Single-wall, and is very long, which is important for me as a tall dude. I had a BD Firstlight at one point and sold it because my head and feet were jammed against the walls. I need a long tent. Also, I like that it has a zip-out section in the floor for digging snow, cooking, getting into the tent with your boots and crampons on (or putting crampons on inside the tent!), or the emergency midnight pee. Haven't seen that feature in many tents and it is awesome.
Downsides: No vestibule (the tent interior includes the "traditional" vestibule space, which is ok to keep all your gear inside with you), and isn't as bomber as some of the other tents. With the internal guyline kit (makes an "x" over each door) and properly guyed out it is very strong, never had an issue.
Main downside, which is similar to all single-wall tents, is condensation.
But the price point per square footage per pound is good. Again, depending on your intended usage of the tent and if you can afford more than one tent (ie, getting a specialized tent for different trips), you might want something else. But this is a good all-around winter shelter.