Gramps in the first place isn't used in a team often, so neither options are particularly amazing. He doesn't have innate star absorption advantage, so he can't really crit reliably enough to use Joint Recital. Heroine Eli-chan is nice, but unless he's solo his NP gain isn't great (1 Arts card).

His ideal CEs are multi buffs CE that has a NP gain effect. King Hassan main usage scenario is soloing, so he can BQA/ABQ for big NP + star gen every turn. CE likes Our Conquest on The Ocean of Stars from CCC, and Pharaoh Chocolatl from Semirami's Valentine are good examples. Alternatively, Iron Willed Training (and Beyond Awakening) are decent options, providing constant damage mitigation, and for Beyond Awakening, buffing all 3 card types to maximize his BQA chain's effectiveness.

If you insist on using him in a party, Heroine Eli-chan, and down the line, Aerial Drive (from Halloween). Talks of Hot Sand is also a solid option, you're given a free copy through the Chaldea Boy ticket, and it gives him the star absorption needed to reliably crit in a team.