So, I need advices: I already have Waterja R4, Ruinga R4 and Quake R3. I'm running low on 4* Black Orbs. Which is the next -ja spell I should hone? I would say Thundaja, but I want to be sure. I should have enough to craft both Thundaja R3 and Firaga R3 (but after that, I'm done with 4* Black Magic until orb conversion).
Keeping in mind if it's a vulnerability boss 19 times out of 20 Thundaga with decent gear/levels will get you 9999 anyway (along with Attunement II, etc.) it actually skews away from "what element has the most vulnerable bosses" to "what element is absorbed/resisted the least"
Thundaja seems to get the most use in either case, although in support of my point above and directly relevant to current content, Thundaja is also one of two r4 black magic spells (the other being Bioga) that's useful for Ogopogo elite, if you want to run a caster group and bounce stuff off Reflect.
(p.s. repeating for new page - Barnabas is also there for all your sustained BM 4* orb farming needs, at least until the new dailies and/or orb conversion hit anyway)