An all-mountain snowboard is designed to handle just about everything the resort throws at you—groomed runs, trees, park features, and even some powder days. It's the most popular category because it gives you one board that works across all terrain without being overly specialized.
If you're the type of rider who likes to mix it up—carving groomers in the morning, hitting the park after lunch, and exploring off-trail when the snow's good—an all-mountain board is your best bet. It's also the smartest choice if you're only buying one board for the season.
The trade-off is that an all-mountain board won't outperform a specialized board in any single category. A dedicated freestyle board will be more playful in the park, and a freeride board will float better in deep snow. But for most resort riders, the versatility more than makes up for not being the absolute best at any one thing.