Definitely the gracalaria hayi, which I got from you guys at Reefalpaooloza in Jersey 2 years ago! I used to have a fox face that decided to devour the halymenia maculata, it was a nice suddle contrast while it lasted, lol.
Halimeda is one that looked very nice on the floor, between the sand and rock, but has not done well for my tank for some reason...
I know Halimeda needs high calcium and alkalinity. I'm giving it a shot. I hope it works out.