Unless you want the difficult terrain or are dealing with targets resistant to fire, Erupting Earth is generally inferior to Fireball IMO:
- Damage doesn't surpass fireball until 6th level (and who is going to upcast using a valuable 6th level or higher slot?? There are better spells at those higher spell levels...).
- Cannot affect targets more than 20 feet above the ground. FB can affect a target nearly 170 feet above the ground.
- A bit shorter range (EE 120 vs FB 150)
- A much smaller AoE (see diagram below) for 20' cube vs. 20' radius sphere.
View attachment 156863
Now, I am not arguing against EE being a great spell when needed, but I think the argument for it being better due to damage at higher levels is fairly weak since it
barely surpasses FB at 6th level (by just 1/2 a point!) and doesn't see serious increases until 8th or 9th level slots! And, as I mentioned above, who would use such high-level limited slots to upcast a 3rd level spell? Frankly, extremely few games even get to the level where you can even
cast 6th or higher level spells.