Go with Satan.

Ea doesn't get a lot from her awakening.
The echo burst effect is a positive, but not a difference maker yet.
Cooldown reduction on her nuke/rage shave probably doesn't really impact advents all that much. And even if it did, you'd have to rush to lv 65 to pick that up. It's more useful against Wrath ult when fights get long enough and you cycle through the modes a bunch of times.
The +combo buff on her dimension barrier is also a positive, but not a huge difference maker. And you still have to rush to 75 for it.
The change to the stun punisher is only meaningful if: the enemy stays stunned after the first buffed hit OR the fight lasts long enough for the enemy to be stunned multiple times. So it's mainly for union events. More specifically, Wrath.
Gee, we just had Wrath recently, didn't we? And we're not going to see Wrath again until next April? Hmm, what does that mean for Ea's utility...

Now note this: I have awakened Ea. The most I ever really plan to use her outside of Wrath is off the bench in case someone dies during raging, so she can come in and shave right away. And my water roster isn't exactly strong in the first place. As soon as I actually get another decent SSR, Ea's gathering dust.
I say this with tongue in cheek, but it's true. The best thing that resulted from my spending the eyes to awaken Ea was drawing Uriel from a ticket later. That I spent eyes to provoke the rng to give me another kamihime on the awakening list. (and Uriel's awesome, so it worked out for me)

Moreover, after Horus, there's another drought of fire events. The next fire event is a tower quest in the end of November. And for non-tower quest events, the next fire event is Iwanagahime, the new year's advent.

At least if you awaken Satan, you'll have this event plus the next one to level her up in time for the Phoenix reprint. And then sometime before the fire tower quest, Pride runs again.

Oh, important thing: I have/had eyes to spare, so I could afford to awaken Ea at the time for silly reasons. If you only have 3 eyes, don't even think about Ea.