Well, I say 'Rail'.
I kinda like the idea that there's a very subtle kink in the pronunciation, kind of like 'Raoul' but with an 'i' instead of an 'o' ('Ray-iel', you might say). But 'Rail' is better for everyone, because god knows, a lot of folks can't handle subtle differences!
I made up the name 'Raile' because I wanted to give him a Japanese surname, but counter it with a first name which would translate horribly into Japanese ('Lail'?! 'Lair'?! 'Rare'?!). I'm pretty sure 'Mizutane' is a word for elves and the Fair folk and soforth (there are reasons I used it), but I can't find corroboration in any online source. If I can find my English/Japanese dictionary again, I'll check.
The girl in this week's strip is saying 'Rai' as in, 'Ray'.