All-mountain snowboard boots are built with a medium flex and balanced construction so they handle a bit of everything—groomers, trees, park laps, and light powder. They're not the absolute best at any one thing, but they don't have any glaring weaknesses either. Think of them as the versatile daily driver for resort riding.
If you spend most of your time at the resort and like to explore different terrain rather than specialize, all-mountain boots are probably your best bet. The medium flex gives you enough responsiveness to carve and stay in control at speed, but they're still forgiving enough for occasional park hits or sloppy landings.
They're also the safest starting point if you're not sure what type of rider you are yet. Many snowboarders never move past all-mountain boots because they simply work well across the board. Just keep in mind that if you end up riding park every single day or chasing steep backcountry lines, a discipline-specific boot will eventually serve you better.