I prefer the sound Eli but the completeness of Ethan. So I would go a third option: Elias or maybe Elijah.
I also think with an E last name, it’s about flow to last name. Some E firsts will be easier to say than others with alliteration, syllable count, and an I (Eli) versus say an N ending (Ethan).
If only these two, would go Eli as it’s more spunky and friendly to me but Ethan’s very reliable.