I think I prefer to [name_u]Aiden[/name_u] spelling, but the fact that [name_u]Aidan[/name_u] is the traditional Irish spelling makes me want to use it.
Also, do you think that [name_u]Aidan[/name_u] looks slightly more masculine than [name_u]Aiden[/name_u]?
[name_u]Aidan[/name_u], by far! I just think it’s nicer looking, and [name_u]Aiden[/name_u] looks trendy or misspelled. It looks like a name rather than “aide” with an “n” tacked on. I see what you’re saying about it being more masculine, too - it’s more in the vein of [name_u]Eden[/name_u] or [name_u]Arden[/name_u] than [name_u]Aidan[/name_u] is.
I personally prefer [name_u]Aiden[/name_u], I like the softer look of it and as it is so popular and I wasn’t familiar with the name before, it also doesn’t look like a misspelling to me.