AY-den is definitely the most common pronunciation for either of those spellings. I haven't met an
Aiden that pronounced it EYE-den. even the original Irish,
Aodhan, is pronounced AY-den.
With the extreme popularity of
Aiden and all it's variants, if you wanted to pronounce it differently than AY-dan, I'd spell the first syllable differently to avoid headache, unless there is a family reason to keep the spelling (ie honoring an ancestor).
Eiden is kinda cool. I couldn't find a real name that was pronounced EYE-den. Just AY-den and EE-den.