Medium-soft flex boots (rated 4–5) are a great match for exactly that type of riding. They give you a bit more structure than a pure park boot, which helps with control when you're cruising groomers or exploring the whole mountain, but they're still soft enough to keep things playful in the terrain park.
This flex rating sits in that sweet spot where you can press and butter without fighting your boots, yet you'll still feel responsive edge-to-edge when you pick up speed. It's especially popular with intermediate riders who are progressing beyond beginner gear but aren't ready for the precision—and stiffness—of a freeride boot.
If you're spending most of your time lapping the park, you might prefer going even softer. But if you want one boot that handles park laps and all-mountain cruising without sacrificing too much in either direction, medium-soft is a solid pick.