Use Samsung or Google account for automatic backup?
If you are going to switch phones to another Samsung brand in the future, use the Samsung backup.

If you switch to a different android phone manufacturer, then use Google backup.

However, there is no reason not to use both. All of the Google service stuff, to my knowledge, does not backup with Samsung, and vice-versa.

As for restoring apps and data, I do not think they will collide.

You could also change what each is backing up. Say for instance, let Google save off the Apps and other google service things, and let Samsung do the rest.