Who played a better Synth? Kirsh or Thia / Tessa?

I thought Elle Fanning as Thia was unimpressive, too emotive/emotional for a synth, but I was blown away by her Tessa. I kept seeing shared mannerisms/gestures/postures with Kirsh from A:E and Ash, Bishop, others. Really impressive. To absolutely nail the rendition as one character, and then intentionally not get it right with another, single actor, single movie? Very impressive and clearly intentional.

I hated Kirshe

Kirsh is a Prodigy synthetic, not a Weyland-Yutani synthetic. There did not appear to be any Weyland-Yutani synthetics in season one of Alien: Earth.