I like them both too. They're popular and overused but they still sound charming to me, they're friendly and innocent.
On paper I like
Aiden more, but after saying them out loud I might actually prefer
Ethan.
Partly because
Ethan always sounds the same while whenever you say
Aiden you have to choose whether you're going to lengthen the "
Ai" in order to pronounce the "d" or keep it short and use a glottal sound between the "
Ai" and the "en".
Also, when I say them out loud, I think of
Nathan which I'd probably prefer over both of these. But something about starting with a vowel does make those names sound more innocent/youthful and that's part of the appeal of
Aiden and
Ethan specifically.