Nyxthos, Shrine to Nyx is the extremely powerful mana engine of the first "best deck" in Pioneer
There's arguments to be had both ways, but if you can't see any way you'd be able to pay the upkeep, then you shouldn't use the spell
If you want to dive more into the discussion of card advantage vs card quality, I cover this in my discussion of the best black Commander tutors in Magic when discussing the power of Imperial Seal and Vampiric Tutor
Aragorn, the Uniter More often than not, Aragorn, the Uniter is used as an aggressive creature due to its focus on offensive strategies, with abilities that trigger whenever you cast red, white, or green spells
He provides unconditional removal that every color can access and brings back all the permanents he exiled to give you a massive head start in the new game