Is there a point to posting this if the JP devs aren't going to be reading the EN forum? Well, jic:

The healer trusts (if you don't have the unity ones, then at least Kuipipi and Karaha-Baruha) are especially useful.

Koro-Moru, KoH and Arciella are great for haste and refresh

Kupofried and Qultada's corsair's roll are a must-have for exp/cp

August and Amchuchu are the best tanks (I'm not a fan of Ark-EV but I guess some like her)

Shantotto II as best dd trust

And then there are those with niche uses:
-Selh'teus for keeping the party alive during bad aoes
-Zeid II for reliable stuns
-Nanaa Mihgo for TH and getting extra drops from her random steals (Ark-MR also for TH, or Aldo for an extra 'bully')
-all the DNC trusts for ja proc'ing in Dynamis
-the BRD trusts if their default songs happen to be useful for you
-Star Sibyl for extra nuking power
-Ark-TT for sleepga
-Ferrous Coffin for raise (assuming you're not the only player in your party)