Unlike a lot of other modal spells, neither of these options feels significantly better than the other as I frequently see Commander games where either one would be a good option to have
The idea of playing Worldfire on turn four or maybe even earlier is pretty appealing - just think how many more matches you could fit in now that each one takes just 20 minutes
Nowadays every archetype has a billion support cards so you can build a 100% on-theme deck: if you build Goblins then every creature in your deck can easily be a Goblin, your commander will obviously buff Goblins, and even the noncreature cards will be referencing Goblins
Put this card onto your Active Salamence
Turn it face up any time for its morph cost.) When this creature is turned face up, you may exchange control of target creature you control and target creature an opponent controls
Memory Vessel has received a minor update to clarify that players can play only cards they exiled from their library during the effect of the activated ability, not the Memory Vessel that was exiled to activate the ability