Of these three, I'd have to choose
Hilary. It's my stepsister's name and I've never liked it. I had to bite my tongue when my stepmother once mentioned how much she loves it (well, obviously she does). I don't like it due to the "Hil" syllable, the rest is okay.
But.
Hester and
Harper are worse. They are just uglier. Every syllable of them is ugly, whereas with
Hilary it's only the first syllable. And
Hilary at least is not old-lady ugly the way
Hester is or trendy-surname ugly the way
Harper is.
So if forced at gunpoint,
Hilary it is.