Which should be my first-go-to Exeggutor?

Whichever one of the E/SoB ones you fast-TM to BS.

Don't change the one with Confusion. I would TM both 98% ones to BS. I wouldn't touch the low IV ones at all...say hello to the professor...

Level 35 good IV Eggs are a great way to get your foot in the door for raids. I say that they're great specialists and not great generalists, so use exegg candy on them and save Stardust for legendaries, dnites, ttars, etc.

My exception to this would be that 2,481 CP Exeggcutor with a very rare and powerful legacy move. Confusion on an Exeggcutor is absolutely monstrous on gym defense and decent against certain bosses.

This morning I actually bothered to solo Omastar and it had double water--weather not a factor either way...2168 SoB Vileplume; 98% 2722 BS/SoB Exeggutor; 2554 C/SoB Exeggutor; 2510 C/SoB Exeggutor; 2302 Sceptile FC/Leaf Blade; didn't use 2026 Victreebel in 6th spot. 1st try won with 8-9 seconds left.

Double grass your 98% and think about putting just a little more into it

i'm with rest, don't change confusion but everything else should be bullet seed. nothing wrong with eggsasensory but plenty of other, better options there including the nice cheap espeon.