Though these two cards are essentially the same, I favor the Hoof because of cards like Green Sun's Zenith and Natural Order
It rewards aggression and reckless abandon, and it gives you a reason to play pump spells in a format that otherwise has no interest in them
We liked the idea that you had the option to cast the spell for less mana like evoke, but also the layaway creature from Adventure
Then you can +1 him to make your dork unblockable and then also draw and discard
Ugin's Labyrinth helps smooth out early draws by providing a quick mana boost for powerful early game interaction like Chalice of the Void, which can shut out some strategies altogether
Kaalia lets her controller cheat on mana and get those creatures into play as early as Turn 4 (without ramp and with a Haste provider, like Lightning Greaves) and even sooner with mana acceleration, like Sol Ring