I suppose I already know this, but Sol should be my first MLB right? I mean I haven't been playing for long so I don't even have Eyes yet, just 5 or 6 shards. But I assume even before awakening she's worth using the only 5 golden books I've got.
Edit: I've got Gaia which also has an awakening, but I assume she is less of a priority (topped with the fact I have little to no wind anything, weapons or Eidolon.)