Less confidant players rarely take it and sensibly so
Green has reasonable access to card draw, its got the best creatures, the best ways to gain a mana advantage, and its even got decent removal with fight effects like Primal Might and artifact and enchantment hate like Nature's Claim
Brawn Brawn is a classic trample-granter with a simple way of granting the keyword
You get to choose of course, though the trade off seems worth it
This doesn't hurt your mana too much since it can give you the mana you need for spells, which you're going to have a ton of -- and it can permanently become a creature in the late game
The most impactful card is probably Exterminio, which would translate literally to Extermination but probably references to Overkill, the mechanic from Final Fantasy X, . Exterminio is a black instant removal spell with an interesting twist: setting a creature's health to -9999 plays around indestructible