[x][Travel] Discreet.
[x][Train] Develop New
-[x][Develop] Sustituto(Substitute)
Man, we just have no luck fighting tanks, do we? Thankfully, most Bleach characters fall firmly under Moar Speed, Moar Power, or Moar Conceptual, and there are very few actual tanks.
As for our our trip into Hueco Mundo's upper atmosphere, I say stealth. No need to give Aizen any advanced warning that shit is freaky regarding that one caterpillar. We'll have plenty of other chances to practice Fuego Mistico since we still have unfinished business with the Forest Guardian.
And finally, I pick the Bunshin no Jutsu. A nice clean way to escape hits and make getaways should we need to, something we distinctly don't have. A new attack would be nice, yes, but we just got awesome control over the most outright destructive of the classical elements and the quintessential Fuck You Beam that can be hyper-specialized more than any other vanilla Hollow Technique I can think of. We're already loaded for bear, so why not increase our ambush power?
Edit: I also find the Highly Visible Ninja route to be absolutely hilarious, and really want to see fuckers get ambushed by a goddamn living sun that they somehow never saw coming.