When you select a repeat grid object, you can see pink highlight if you mover your cursor between grids then you could just drag it to modify the padding.

With Stack, you have to double click to edit padding, which feels unintuitive and inconvenient. 1. You'd easily miss the fact that the particular group is stack enabled so you can drag the padding. 2. When you're working on page layout, you'd be repeatedly double clicking the group especially if you have many objects on the same artboard.