First I’d like to ask, “better for what?” It’s always a good idea to find out what the ultimate goal is before deciding on a course of action.
That said, I agree with Karin. Running on sand is definitely more challenging from both an intensity and stability perspective. But that isn’t necessarily going to be appropriate for everyone. Also, if someone is training to run a race which will be on concrete, running on sand may not be the best way to train for that goal.