So WoWhead says that Aftershock is best. It is very nice when the 25% chance pops but it rarely pops for me (maybe just bad luck). But with Elemental Blast it does decent damage aswell as rewards alot of Maelstorm. With only a 12 second cooldown as well so instead of rarely popping two earthquakes from Aftershock. I can just build Maelstorm with Ele Blast, Chain Lightning and all the Maelstorm building abilities from my covenant. Seems a tad counter-productive to rely on RNG. Though perhaps I haven’t experimented with it enough, looking for some advice from the community. Thank you in advance! 
Edit: I am starting to see that with cov passives plus spamming Chain-Lightning and Earthquake I can do some top notch AoE. Still up for advice and discussion
aftershock is best with echoes of the great sundering, so you can pop earth shock and if you get the aftershock buff, you can then press earthquake, but in the end, if you prefer to use elemental blast, you should play what you like
If you’re talking AOE for pushing M+ content, AS provides you the greatest DPS opportunities with the EoGS legendary equipped because you should really only be casting Earthquake when it’s empowered by your Earth Shock. EB just isn’t as valuable in AOE or M+ situations where you’d benefit more from casting CL and your ES/EQ combo. So that’s the theory behind why you see AS as the recommendation. There have been times where I get lucky with 2-3 back to back AS procs in an AOE situations and it’ll rip. Yes it’s RNG reliant but the potential benefits outweigh EB in my opinion.
Raid would be different. You’d want to keep EB for the boss fights.
In situations where there are many targets, you can get a lot of MS using CL, so you don’t need EB. Damage cannot be expected much compared to CL.
If you don’t have EB, you can’t get a lot of MS in the ST situation. this talent line is a very important line for ele. Which one to choose between AoE or ST.
Yeah I am sticking with AS for the AoE potential you are talking about. After playing with it in dungeons you are right it is top notch AoE damage. With the multiple targets I just use CL for the MS and so don’t really require the MS reward from EB. It has its downsides while solo questing not having EB, but it’s a much bigger draw back for AoE building. And I am trying to gear and build for M+