Enemy boba reinforces, use tfp's special to force a counter/dodge and enjoy your win.
Phantom 2.…. Can be problematic, if the AI uses it's stealth special you should be right, if it doesn't & it takes our your Biggs you may be in trouble.
I think Vader as a maxed reinforcement is amazing.
Poe as a maxed reinforcement is also brilliant.
Reaper still has it's place despite the nerf.
Sun fac as a reinforcement is also amazing with possible double-stun combo.
So many good possibilities it's hard to tie a few down as the 'best'.
Not to mention if RNG hates you, no reinforcement can save that battle from a horrible loss.
