Changing T-5 transmission fluid - Royal Purple Max ATF or Royal Purple Synchromax?

Max ATF -- Recommended for all applications where Ford MERCON® / GM DEXRON® III transmissions fluids are specified. Provides outstanding rust and corrosion protection.

Synchromax -- Recommended for manual transmissions that specify automatic transmission fluid, multi-viscosity motor oil or straight grade motor oil.

IOW, I don't think it's going to matter. If it were me, I'd go with the Max ATF.