Merit according to how you play is the best to describe it seeing how it's your membership, yes.
But, if you want some tips, Store TP and Overwhelm is the best to 5/5 just for the general output.
Now for myself I did
5/5 Store TP
5/5 Zanshin
5/5 overwhelm
1/5 shikikiyo
3/5 Ikishoten
and I still haven't decided to the last into Blade Bash or 4/5 Ikis.
Now I was a SAM for a while but I didn't put much thought or merits b4 the new update, only had 5/5 store tp and 5/5 overwhelm then focused on other jobs so that's why I have it on zanshin/Ikis and I do have to say... TP comes in quick enough that a couple times I was able to self WS w/out Meditate or a premature Sekka (yes, it has happened a few times ._.).
Mind you, it was a rare lucky streak but still blew my mind away.