You can define largest in several ways: largest vertical drop, uphill lift capacity, highest elevation or most skiable acres (on 1 lift pass). I will rank the top 7 (because 2 on the list are on a combined lift pass) using the last method as it seems to be the best way to relay the largness of a resort, and I'll include other statistics.
1. Whistler Blackcomb (British Columbia, Canada) - 8,171 Acres - Highest Elevation 7,494 ft. - Vertical drop 5,200 ft.
2. Big Sly/Moonlight Basin (Montana, USA) - 5,512 Acres on a combined lift pass (Big Sky 3,812 ft./Moonlight Basin 1,700 ft.) - Highest Elevation 11,166 ft. - Vertical drop 4,350 ft.
3. Vail Resort (Colorado USA) - 5,289 Acres - Highest Elevation 11,570 ft. - Vertical Drop 3,450 ft.
4. Heavenly (California/Nevada, USA) - 4,800 Acres- Highest Elevation 10,067 ft. - Vertical Drop 3,500 ft.
5. Snowbird/Alta (Utah, USA) - 4,700 Acres on a combined lift pass (Snowbird 2,500 ft./Alta 2,200 ft.) - Highest Elevation 11,000 ft. - Vertical Drop 3,240 ft.
6. Lake Louise (Alberta, Canada) - 4,200 Acres - Highest Elevation 8,650 ft. - Vertical Drop 3,250 ft.
7. Squaw Valley (California, USA) - 4,000 Acres - Highest Elevation 9,050 ft. - Vertical Drop 2,850 ft.
Extras
Highest Vertical Drop - Revelstoke (Alberta, Canada) 5,620 ft.
Highest Ski Lift Elevation - Breckenridge (Colorado, USA) 12,840 ft.
Highest Resort Elevation - Silverton (Colorado, USA) 13,487 ft.
Highest Average Annual Snowfall - Mount Baker (Washington, USA) - 647 inches
* Powder Mountain in Utah lists over 7,000 Acres but this includes lifts, snowcats and back country access.
Killington, Vermont rules in the East. It has more lifts, runs, and more skiable terrain than any other ski area in the region. Whiteface does have 400 feet more vertical, but Whiteface is a smaller area with 70+ trails (compared to 200 at Killington), a third of the lifts at Kton, and about 2/5 of the acreage of Kton.
Vail Colorado is the largest single mountain resort in the USA with a vertical drop of 3500 ft, 200 trails, 34 lifts and 5280 acres of pristine snow for your skiing and riding pleasure. Big sky and moonlight basin may be larger, but it's two mountains not one. Technically Vail CO has three peeks (Wildwood, Two Elk Lodge and Patrol Headquarters)
Revelstoke Ski Resort, British Columbia
Revelstoke vertical drop based on highest and lowest point is 5997 ft
Located in the Rockies in Canada, Revelstoke is the tallest ski area in North America
It is the largest indoor ski resort but it is not nearly as big as most outdoor ski resorts.
The largest ski resort in France and in the world is Les 3 Vallées with 600 km of piste. For more information look at the question "What is the world's largest ski resort?"
Les 3 Vallées. For more information see: "What is the world's largest ski resort?"
the biggest ski resort in the us is big ski ski resort in Montana it is also the second biggest in north America
Paradiski
France. For more information see: "What is the world's largest ski resort?"
Snowmass, Colorado
Whistler Blackcomb
Paradiski.
600 km of interconnected piste in Les 3 Vallées. For more information look at the question "What is the world's largest ski resort?"
Vail
Val Thorens is Europe's highest resort, also in the Three Valleys, the largest ski area in the world.