Various modernised spellings exist for Old English words containing the letter Æ and æ for example Ætheling can be modernised as Etheling, Aetheling or Atheling.
Is there a reason to prefer one modern spelling over the others when not using the actual Æ/æ letters?
P.S. A friend of mine intends to give their newborn baby girl an Old English middle name (specifically Æthelflæd) and it would not be possible to put the Æ character in her passport, so they are stuck between the two most common modernised spellings (namely Ethelfled and Aethelflaed) while also knowing sometimes Æthel is modernised as Athel as in Athelstan, and they were just deciding between these.