User blog:Nicholas0524/Darvenshel or Oulu?

When I am watching some JP player challenging trial no.3, it seems like JP player prefer Oulu more than Darvanshel? (I am not sure, but most of the video I watch they use oulu, I might be wrong.)  Therefore I am pretty confused. Because from my understanding, by choosing Darvanshel as the leader can free up a space in your squad by not choosing Melchio, and by this we can choose unit like Zelban which give us a huge boost in Def, which should be more beneficial than Oulu 20% boost in HP and Def. Moreover, we don't even need to worry about keeping Melchio BB up. Now I am prepareing my squad 2 against Maxwell and I just want to know, which unit I should lvlup, Oulu or Darvanshel?

Btw, is Tech Gizmo2 useful for Darvanshel or are there any more useful sphere? I just want to keep his BB always up.

And If you need a Darvanshel(Anima, max lv, SBB lv5, Legwand Gem and Tech Gizmo2) leader, feel free to add me, my ID is 3628802678, I got a max.lv, max SBB. Lilith and Grahdens too.