The Saitaris is our favorite four person winter tent for base camping or long expeditions in nasty weather. When compared to the competition from Mountain Hardwear, The North Face, and the like, the Saitaris is the shining star: it uses much better fabrics, pitches faster and easier, has much better ventilation, and is likely much tougher. For details on its fabrics and materials read the Hilleberg Tarra Review.
The Saitaris' primary competitor is the SlingFin Hardshell, which is slightly less spacious but stronger, 2 lb. lighter, and costs $300- $500 more depending on pole type. We haven't used both tents for long enough to have a conclusive recommendation for when to use one tent or the other. Our preliminary suggestion is to opt for the Saitaris if comfort is more important than Herculean strength (the Saitaris' vestibule is much larger than the HardShell's but the HardShell is perhaps the strongest 4 person tent in the world). In short, choose the HardShell if your primary application is high altitude mountaineering and the Saitaris if want to do that plus a bunch of base camping in more forgiving environments. Both tents are world-class.
Several people used the Saitaris and Hilleberg Jannu for a ski expedition in Greenland. Here's their brief report:
"[Of the tents used] The Saitaris blew us away the most. It is relatively light (for being a four-person expedition tent), unbelievably spacious, and so quick to pitch thanks to its design that enables the user to keep the fly attached to the body. We would tag team that tent and get it up in less than five minutes…and that's with burying snow stakes for all of those guy lines even! It has such a thoughtful design; from the efficient use of vestibule space to the clever guy line arrangement to the red of its fabric (the warm color makes it seem nice out even in the middle of a blizzard!)