[bladeofdarkness]

in truth i would (and do) prefer the ayu ending
as much as i love nayuki (yuki no shojo is my ringtone) ayu is the one girl that embodies elements from all four of the other characters

Spoiler for aspects:

the family problems that nayuki faces later on, as well as the "childhood friend" aspect
the ability to produce miracles that mai has (this plays a huge part later on)
the medical complications that shiori has
and makoto's "non-human" status

ayu's character contains aspects of all 4 girls
and in my mind this makes her ending the best one