I have two older rigid mountain bikes. I think either would be great as a commuter bike to ride around a college campus.

1995 GT Outpost Trail with Shimano Altus components. 1991 Nishiki Kodiak with Shimano Exage 300 LX components with the Shimano biopace crank.

I've had the GT since it was new. It has always been stored indoors. The Nishiki was a recent Craigslist find that has clearly been exposed to the elements in its lifetime, but has cleaned up well.

Based upon the bikes and their respective components which would be the better bike?

I can't decide which one I like better and I'm trying to decide which would be the better one to keep with me where it is stored indoors and which one I should give my son to take away to college where it is going to end up exposed to the elements chained to a bike rack outside of dorm.

Any suggestions?

The Nishiki is less likely to get stolen.
The GT is a better frame.

Both are heavy, but for commuting, both are tough.

Keep the GT, let the Nishiki go to college.

6 of one, half dozen of the other.

An Outpost was pretty entry frame with a PG 4130 seat tube and hiten stays and remaining tubes. The Nishiki probably has less name brand awareness.
Keep whichever fits you best and you like the most.