Cheaper for memory, not for pefromance.
Performance of sphere requires computing with PI which sure, its quick, but possibly mote expensive depending on pi digits.
As far as collision cost/sweep the only answer is that you have to use whatever works for your project and bench test along the way.
You can get some obvious cost reduction by reducing the number of primitives involved in a specific object, or outright changing the primitive.
But the only way to know is to check the specific situation.