Quote Originally Posted by VeryVoodoo View Post
Anyway the simple answer is if you're new with underdeveloped grids (i.e. your wpns don't have SLs on 'em), the 40char%/20%hp will likely help you more with most content.
And if you're a player with fully developed grids, or mostly developed even, you'll want the elemental atk↑ eidos then for better dmg.
If you're using a +100% elem ATK eidolon in either slot, the HP/char ATK eidolons become pretty attractive.