Here's my plan for how I'd like to form each CW/UW combiner:

Superion: the five UW figures, plus CW Powerglide, fights Menasor

Convoy Grand Prime (instead of Ultra Prime): the five UW figures, fights Grand Galvatron

Defensor: the five UW figures plus, CW Groove (don't care if that leaves me with two Grooves), fights Bruticus

Sky Reign: CW Sky Lynx and his four Autobot gentlemen, fights Galvatronus

Victorion: the six CW figures who combine into her, fights Devastator (makes sense for the super special fan character to go up against the biggest bad guy)

G2 Superion: the six figures who combine into him, fights G2 Menasor

Battle Core Optimus Prime: single figure by himself, plus CW Rodimus, borrows Convoy Grand Prime's limbs to become Optimus Maximus, fights Grand Scourge

Menasor: the five UW figures plus, CW Blackjack, fights Superion

Galvatronus: CW Cyclonus, CW Alpha Bravo, CW Offroad, CW Rook, and CW Blast Off, plus CW Viper, fights Sky Reign

Devastator: the five UW figures, fights Victorion

Bruticus: the five UW figures (once Takara gets to doing Bruticus), plus CW Shockwave, fights Defensor

Grand Galvatron: the five UW figures, fights Convoy Grand Prime

G2 Menasor: the six figures who combine into him, fights G2 Superion

Grand Scourge: single figure by himself, steals limbs from whoever he wants to form Grand Scourge Hyper Mode, fights Battle Core Optimus
No interest in getting Scattershot right now.
And leaving out Predacus and Thunder Mayhem. But if I were to include them, I could have Galvatronus switch sides (since IDW Cyclonus isn't fully evil in the comics) to fight Thunder Mayhem and Sky Reign could fight Predacus.