Definitely Snowshoe. High elevation with plenty of natural snow. They even have decent powder sometimes, which is pretty rare for the Mid-Atlantic. Also, it's an Intrawest resort, so it has a very nice mountain-top village, with plenty of modern, ski-in/ski-out accommodations to choose from. The downside, is that it's a bit of a hike - probably too far for a day trip. Ditto for Canaan Valley and Wisp. If you're willing to drive 3 or 4 hours, I'd say Snowshoe is the best overall.
Closer to DC, the big three are Whitetail, Massanutten & Wintergreen. Of these three, I like Wintergreen the best. It has some fast lifts, and more advanced terrain. It's also higher in elevation, so the conditions are often better.
Whitetail & Massanutten are both a little closer to DC, but due to their lower elevations - especially Whitetail - the conditions usually aren't as good as Wintergreen and Snowshoe. Of these two, I'd say Whitetail has better terrain, but Massanutten is usually less crowded.
I grew up in that area, and by far the best skiing is at Snowshoe, but here is the issue, it takes 5 hours to drive there. Snowshoe is not a day trip. In that length of time you could fly from Dulles to Burlington, VT non-stop and drive 30-60 minutes to some of the best east coast skiing. If you want close, sharpen your edges and head to Liberty and Whitetail which are probably the two closest if you live in MD or NW. I never went to VA so cannot comment.
If what you want is more than a day trip also consider Seven Springs, in PA about 4 hours away. There isn't as much vertical but they have good lift capacity and excellent man made snow, probably the best in the region. There is lots to do off the mountain at Seven Springs and it is has a contained feel. Being said it is in my opinion the better option for families, with a really nice indoor pool. bowling, miniature golf, and ice skating all at the resort. There is no need to drive at the resort, only one parking lot. I think the last thing that might push Seven Springs ahead is the night skiing, where at Snowshoe the runs close around 4PM Snowshoe's amenities are the closest thing to resorts like Keystone and Copper MTN in the mid-Atlantic. It also has my favorite run in the region, Cupp Run. It's on par with a nice solid intermediate groomer at most Colorado resorts with a similar amount of vertical.
If you want to go on a multi-day trip, I think Snowshoe in WV is the best resort near DC to go to. Even though it is around 4 hours away from DC, Snowshoe is worth the time, because it has great powder and almost always has great conditions. The conditions at Snowshoe are usually comparable to out west. Snowshoe also has lovely places to stay at the top of the mountain, and some challenging terrain for avid skiers, like me. Another great resort to go to for a multi-day ski vacation is Wisp Resort, in McHenry, Maryland. Wisp has state-of-the-art snowmaking and grooming, and gets a good amount of snow every year. Wisp also has great instructors that are good for any level of skier, and help perfect your skills. The same downside is for Wisp, as in it is around 3 hours away from the DC area. I also think that it is worth the time to go to Wisp. Wisp is also less expensive than Snowshoe.
On the other hand, if you are looking for a 1 day trip someplace, Liberty is the closest at about 1 hour away from the DC area, but is mostly man-made snow and has very few trails. I would suggest you go to Massanutten Resort, because it is about 2 1/2 hours away, but has good snow and many activities to do. Besides the skiing, it has a huge indoor waterpark and many other things. You could also go to Bryce Resort, Wintergreen, or Whitetail, which I've heard are OK.