Did any of you have this system of NS rotations available at your institution? In your experience what were the major differences between these two rotations at your particular school?

In general, a sub-I implies a higher level of responsibility and probably looks better on your transcript. However, I would guess that most neurosurgery programs will treat you the same regardless of the name of the course you register for (e.g., at my institution they wouldn’t even know the difference).

Just make sure the rotation has the same level of responsibility and call as whatever that particular institution considers best for “subI” rotators, and that it is not a watered down experience geared towards students who are not going into neurosurgery.