Which Exeggutor to power up?

Confusion psychic, assuming thats atk/def/hp, it not only has a higher attack, but confusion is just that much stronger

I have 12/14/12 C/SB maxed to 40. That thing is a beast that I find I use more than I think I would. Back when Suicune was a thing, it just tore into it, for example.

I just checked Calcy and 9 months later, it's still in my personal top 6 counters to Suicune.

Neither. There are better psychic attackers. But if you have to do one, confusion is a great move as long as you don't care about dodging.

Neither, I have both & they don't cut it on my Machamp team which will be your primary use for a Psychic attacker. Psychic a poor charge move unless it's on a Mewtwo.