I voted for hard, but I prefer a mix. My magic system has the very scientific aproach, where realitybenders can aproach everything like math and find the most effiecient way to do something, but there are also gods and beings that make little to no sense.
My favorite is a soft magic system inside a hard rule.
One of the gods in my universe, the seven haloed, who derives his power from promisses, each halo representing one of his unbreakable promises. One of these promises is to grant power to anybody, who holds their promises. These granted powers can be anything; simply luck or something based on the promis, helping the person to fullfil their promise. Does this make sense, maybe, but the seven haloed exist on a higher plane, so humans can only guess why this even works.
The promis part is absolut. One misstep and all your power is gone; but whatever the power itself is, is open.
Similar to a soldier, one doesn´t need to understand how the gun works to shoot.