System selector

Choose by ownership and lifetime before convenience.

Need	Use	Avoid when
Placed/spawned world entity with transform, collision, replication, or independent lifetime	Actor	It is only a reusable capability of another Actor
Reusable capability attached to actors	Actor Component	It needs its own transform; use Scene Component or Actor as appropriate
Reusable transform-bearing subobject	Scene Component	It must exist independently or replicate as an Actor
Service lasting for one engine process	Engine Subsystem	State should reset per game instance/world/player
Service lasting across map travel in one game instance	GameInstance Subsystem	Data is world-specific or per local player
Service scoped to one World	World Subsystem	It must survive world replacement
Service scoped to one local human	LocalPlayer Subsystem	State is shared by all local players
Immutable authored definition	Data Asset	The value mutates during play
Rich definition needing Asset Manager identity/load control	Primary Data Asset	Normal direct loading is sufficient
Stateless reusable operation	Blueprint Function Library	The function needs state, lifecycle, authority, or polymorphism
Shared behavior contract across unrelated object types	Blueprint Interface	The caller has no target reference

Placement procedure

1. Name the state owner.
2. Name the destruction/reset event: component removal, actor destroy, pawn respawn, world teardown, map travel, local player removal, or process exit.
3. Choose the class whose lifetime matches that reset event.
4. Decide whether the state is authoritative, predicted, cosmetic, saveable, or authored.
5. Keep authored definitions in assets and mutable instances in runtime objects.

Blueprint versus C++

Prefer C++ for stable shared contracts, custom replication, high-frequency loops, complex math, low-level engine integration, and code that many binary Blueprints would otherwise duplicate. Prefer Blueprint for content assembly, presentation, designer-facing variation, and event-driven orchestration. Profile before converting solely for speed.