Use collections.
Single game object files are OK when it’s something really simple that only needs one game object, but for most things you want to use a collection so you can add multiple game objects as necessary (like in your situation).
You can check out this related thread: Game Object Or Collections - Best Practices
…or this one: Is this ok to use collection instead of game objects?
The only drawback with collections is when you spawn them it’s a little more work to set properties on their objects, but for static stuff it makes no difference.