Hard to say, because they are all good.
However, here are a few that I generally won't pick.
Phodom:
Headbutt
Ultimate Sacrifice
Fradz:
Sword Dance
And that's pretty much it.
I probably will not use ultimate Sacrifice because I generally play on
****. So it would just result in an instant game over until I get Galeoth with Phodom.
I won't be using Headbutt for a similar reason, I wouldn't want to put myself in a bad situation because I lost 10% health. So like in a rare case, where I would use Headbutt, then power heal, except I wouldn't get the bonus health from power heal because it didn't cover that extra 10% health I lost. Which could put be into a very bad position. Not to mention that if I am below 10% health, it will kill me.
As for Sword dance, I generally won't pick this, because both illusory double and power orbs provide more benefits than 300% attack speed. Plus he takes 40% more damage, and cannot move. Illusory double provides some extra damage, and can serve as a distraction. While power orbs buff up Electro Shell, which can provide a prolonged life.