I have both as well, they are pin up with the Snap CG kicked out a little further than the EC.
The Eternal has a smoother motion and I like it on flatter sport patterns
The Snap does just that, snaps of the friction and is great on a THS
when used in reverse:
the Snap tends to be too over/under on a sport pattern especially during transitions
The Eternal on a THS will often drive through the pocket too hard, leaving splits or 9s
both good balls, but neither are benchmark or should be included in a limited arsenal