Hi. It is one is up to You. Both ways should work fine and satisfy Your artistic freedom.
It depends what is hassle for You. Maybe a combination of both methods: one ForestPack for large trees, and multiple ForestPacks for bushes, grasses.
To create large grass fields it is more efficient to scatter big grass patches instead of single blades. But should You want to use the same grass to end with hard cut-off line there could be some "hassle".This tutorial
address the problem.
Maybe You will find this tutorial
helpful as well. It shares some helpful tricks.
Hope this helps.
Best way is to experiment, and feel free to share the tips You discovered along the way.