Who should I grail next?

I just finished max grailing Merlin-sama (nobody on my friend list grailed him yet, but I was soo happy when I got him that I promised myself to give him 5 grail...), and now I have no idea who should be the next one to grail.

My currently grailed servants are: Merlin (5 Grail), Heracles (2 Grail), Liz Lancer (1 Grail) and Papa Kerry (1 Grail).
And the current candidates for grailing: Musashi, Karna, Nightingale, Saberlot, Chloe and Kintoki Rider. +Kerry, but he's already got one...

I have only 6 Grails atm, and I simply can't decide who to give them. I undestand that waifu/husbando>gameplay, but I love all my Servants equally (Merlin is an exception, because he is a living meme), so it's pretty hard to decide.

Or should I save my current grails until I get my current most wanted servant, Edmond Dantes? I mean, his event will comes in a few weeks so maybe I have a little chance to get him, even if I have only 16 SQ and a few tickets atm. But y'know, the if my Hope is strong enough, maybe he'll come home to my Chaldea... (I mean, my luck is EX in the past weeks, so there is a chance to get him with only this much Quartz and tickets...)

So the question is: Should I Grail my current Servants or not? If yes, then who should be that one who get them? If no, then I'll pull for Edmond and decide after then...