I always aim for Lunasa as I find her the easiest. No need to mess with the others when you dont have to...
Hm, Koishi is rumored to be one of the easiest EX bosses so I guess the stage is the real trouble... haven't seen it myself yet though...
Yeah, 13.5 is coming but I'm not too excited... haven't played the fighters yet as I'm still more interested in the shooters... though admittedly smashing faces in with Hijirin sound like fun.