I've preferred the Chevy's for many years mostly because of the eggcrate grill look.
However, if it wasn't for that design I would be going with the GMC's.
In my opinion they are more rare...and you have to like that dual headlight (metal vs. plastic) chrome grill...when it is new and bright.
A '72 Sierra Grande is not always an easy truck to find relative to the Cheyenne Super's...their equivalent.
Regardless, value wise?......it is completely buyer dependent in my opinion.
All good
Coley