Backpacking or car camping? I use an rei 1/2 done for backpacking or my old school north face mountain 24. Car camping I use a Cabelas Alaskan Guide six person. It's a beast. Takes the wind and rain. Great tent. But expensive. So is my mountain 24 when i bought it in 1997.
Rei 1/2 dome. Make sure you seam seal it.
Theoretically, you can winter camp in just about anything, it really just depends on how extreme the weather you're expecting to be. If you're camped up on a mountain ridge with gale force winds and the potential for big snow loads, you need a tent that has lots of poles and a low, round design to keep it from getting crushed. So for that, you really want the Mountain 25 (I have one from 20 years ago).
The NF Mountain 25 is kinda trash. Very heavy for what you are getting, quite small inside. I bought one and the pole bent the first time I set it up.
If you actually are serious about spending the money necessary to get this type of tent you should consider:
1. Hilleburg tent
2. Big Agnes Battle Mountain 2 or 3 (similar structure to NF but lighter and just as strong from a better and more reputable tent brand).
3. Samaya (extremely light, extremely expensive alpinist level tents)
AngeloPappas
