I'm a Julia - feel I got lucky as it feels fairly classic to me, very international but I've only ever met a handful of others, mostly my age or younger than me (early 40's) and of other nationalities too. Julie's on the other hand, I've met quite a lot of - and all the UK ones seem to be about 10 -20 years older than me. It's that Diane/Diana, Louise/Louisa, Helen/Helena thing- the version with the A just seems to have dated a bit less in the UK? I also think Juliet's lovely too.
Sarah is kind of the opposite in that I know LOADS my age (as an 80's kid there was at least 2 or 3 in every class at school) but I have met a few younger ones so maybe not as dated as Julie? I think statistically it was top 100 perennially until a decade or so ago too, so that would bear out it being a very classic name.
Aishling not my cup of tea (not sure I like the sound), so for me out of Julie and Sarah - I'd pick Sarah.