Whatever has the most FLBs. Free to play players don't choose their Grids, they simply build the biggest one they can.Water and Wind are their flipsides, so I'd certainly build one of them. Which one do you enjoy playing more?
For Water, Aphrodite or SSR Nike, debuff haters will tell you to ignore the latter.
For Wind, Gaia would open defensive options but I'm not sure if that's something you care about with Hraes. Cu or SSR Cybele would be offensive options, probably SSR Cybele since you're lacking in debuffs.