After having recently played 3H, I do think Byleth would have the more interesting moveset than Edelgard. Though I'd still rather have Edelgard, because it's not like she wouldn't be unique, and I find her design much better; Byleth's is rather dull imo. Speaking of the initial designs at least, because that's presumably what they'd choose. Though obv of the two, they'd go with Byleth. That's the MC, which is one precedent I do think you can rely on.
All that said, while I enjoyed 3H much more than I anticipated, and I understand why people want characters from games they like, I can't get behind it getting a character at this point. Sure it has potential with which to work, and is a well-received title... but there are no shortage of characters with potential from other well-received titles that have less (often much less) than seven existing characters from the series.
Give those fans some more love too.