Arcane Surge vs Wild Arcana. What's the actual difference?

[Ninijo]

SUP GUYS. It's your crazy gnome friend Ninijo who wants to know...

My terrible reading skills is making it so that i can't tell the difference between those two Mythic abilities. So besides the fact that you need to have a spell prepared for Arcane Surge if you're a prepared caster and you don't for Wild Arcana.

So what else is different between the two? Because Wild Arcana just seems better.

[MC Templar]

From PRD wrote:

Arcane Surge (Su): As a swift action, you can expend one use of mythic power to cast any one arcane spell without expending a prepared spell or spell slot. If you prepare spells, this spell must be one you prepared today (even if you have already cast it); if you're a spontaneous caster, this spell must be one of your spells known. If the spell requires a saving throw, any non-mythic creatures affected by the spell roll twice and take the lower result. If you must attempt a caster level check for the spell to overcome a creature's spell resistance, you can roll your caster level check twice (adding your tier to each) and take the higher result. You can't add a metamagic feat to a spell you cast using this ability.

Wild Arcana (Su): As a swift action, you can expend one use of mythic power to cast any one arcane spell without expending a prepared spell or spell slot. The spell must be on one of your arcane class spell lists and must be of a level that you can cast with that arcane spellcasting class. You don't need to have the spell prepared, nor does it need to be on your list of spells known. When casting a spell in this way, you treat your caster level as 2 levels higher for the purpose of any effect dependent on level. You can apply any metamagic feats you know to this spell, but its total adjusted level can't be greater than that of the highest-level arcane spell you can cast from that spellcasting class.

first difference, whether or not you need to know the spell or have prepared it.

Surge you need to have it available
Wild you don't

Arcane surge gets a large bonus to save difficulty as the trade off for having to prepare or know it.