Who has the best Phoenix zeta

Kanan has the best all around zeta imo

Agreed, Kanaan has the best zeta for the Thrawn event. I had Ezra g10, chopper g9, Kanaan, Zeb and Hera at g8. With arena mods. Tier 6 was difficult for me, so to guarantee the tier 7 win I zeta’d Kanaan. It made the event a breeze. None of my squad even had their health damaged.

The two best Phoenix zetas are Kanan and Sabine, for opposite reasons. And between the two, I'd favor Sabine for much-needed killing power and reduced cooldown on a strong AoE/heavy debuff.

However, longer term, beyond the Thrawn fight, Ezra's is probably the most useful simply because Ezra is the Phoenix most likely to see use outside of Phoenix squad.

Ezra is the most versitable toon in the Pheonix squad, and his zeta is useful. He's certainly an option.
Kanan's zeta is a way to shore up one of the greatest weaknesses the Pheonix squad have - a lack of an aoe cleanse. It's very useful in the Pheonix squad, but completely useless in any other situation.
Sabine's is pure damage. Since it relys on debuffs landing though the potency check, it's pretty useless in the Sith raid, but it can bring big numbers in HAAT.
Zeb's and Hera's zetas are fine, but lower priority imo.

Kanan has the most useful zeta in phoenix.

Ezra is the most useful character outside phoenix so his zeta is likely to payoff in other areas of the game.

If theres a jedi rework which brings jedi into the meta ezra is almost certain to be in a top jedi team so his zeta may even be arena meta in the future,.

I'm w/ kanan as well...

However, as a standalone toon, Ezra may be the better choice (& I find kanan useful for carrying low geared toons in TB)