Which book title should I use?

Hammered Hearts: this ones the best to me.

Empty Eyes: nah that sounds more like a zombie book tbh

Stand in the Rain: does it have to do with rain? You didn't mention rain or anything of the sort even though I think it's a metaphor.

In the Dark of Nightmares: no. Doesn't grasp.

Hope this helped!

May I make a suggestion?

Your main character is names Sage Crimson (which is a little cheesy but if you have a young target audience it shouldn't be a problem), and based on her name I think a better title would be Green and Red, or Red and Green, or Red with a touch of Sage (since red implies blood).

The other titles are somewhat cliche. Titles that sell are either one worded, random, or unique to the story. But of what you've given, I like the sound of "Hammered Hearts"

I think Empty Eyes or Hammered Hearts. The other two titles seem quite long for titles but it's up to you which one you go for. Good luck!!!

Maybe you could call it "In the Light of Nightmares" since it seems to fit your story better. Vampires are usually considered scary or negative characters in the world of stories, so they would represent the so called "nightmare" in your title. But, the "light" of it all comes from her true love for Mason. Therefore, there is a light among the nightmares. Just a suggestion

I prefer in the dark of nightmares.

Stand in the rain