Card Mastery Advice!

Right now, I make \~500T coins/day. Currently bouncing between Champs and Legends and I would like to stay in Legends.

I've unlocked 6 card masteries and I'm eyeing what I should focus on next. I have:

* lvl 3 Intro Sprint * lvl 2 RPC * lvl 2 Second Wind * lvl 2 Damage * lvl 0 Super Tower * lvl 0 Cash

I'm considering unlocking the following next:

Econ

* Enemy Balance * Wave Skip * Wave Accelerator * Orbs

Damage/Survivability

* Ultimate Crit * Demon Mode * Nuke * Slow Aura

With GComp, I have perma-BH and perma-CF, and GT/DW cooldowns are at 100s.

I don't want to be foolish and spend 1000 stones on a nothing-burger of a mastery, so I'd like the community's advice. What should I focus on?