Nissa, Worldsoul Speaker has definitely caught the most buzz of the bunch
When it comes into play you get to draw cards, with the downside of losing life, equal to half the number of artifacts you control
Whether its a sorcery, a creature with an enters-the-battlefield ability, the loyalty ability on a planeswalker, or even just an instant that your opponent is forced to cast main phase because they were tapped out on your turn, there are a multitude of ways your opponent could remove your permanent on their turn for roughly three mana
This is a pretty massive ability because it means you can stack flying, trample, and other counters in addition to +1/+1 counters to make a one-shot monstrosity that doesnt ever really go away
Its strong with threshold and unplayable without, as you cant even target the land to be destroyed
These two things combined will likely help Terapagos ex hold up in value in the long run