I have been a skier and snowboarder for 20 years, and have hit nearly every mountain in the continental US, as well as a couple on the eastern side of Canada. From New England to Colorado, up to Washington, Oregon, and Utah, and down to New Mexico and Lake Tahoe (where I now call home), Mammoth is by far the best mountain I have ever ridden. The annual snowfall is ridiculous (I have snowboarded there into July on more than occasion), and the amount of warm sunshine combined with their awesome and well-varied terrain are unparralleled. You can find everything you could possibly want all in one place - from steep chutes and wide open bowls to fast or easy groomers, not to mention the best terrain parks in the U.S. There is a good reason why so many pro skiiers and boarders call Mammoth home.
Yes, it can get crowded at the lifts on weekends/holidays, but the mountain is so huge that you can always find yourself nearly alone on the trails. And should you decide at some point during your day that there are too many people, you can head over to nearby June Mountain (Mammoth lift tickets are good there, too) and find much of the same terrain, and excellent park features - minus the tourists. Every time I've been there, I've had nearly the whole mountain to myself.
You can waste your time, money, and efforts visiting other resorts, but for anyone who is seriously in love with their snow sport, nothing compares to Mammoth. I have been too many times to count, and still am able to find new areas and features every time I take the 3 hour drive down there. It's impossible to get bored at Mammoth.