Choosing a wig shade is difficult, I have trouble with it too haha
What you should always do, in my experience, is choose a shade that will flatter your skin tone over being exactly the same color as the references. It will make the entire costume pull together better and look true to life if you can get a shade of blonde that is blonde but has undertones that work with your face.
The first thing you should figure out is whether you have a warm skin tone or a cool one. There are lots of ways of figuring it out that you can find on the net, but they're not always accurate (for example I have medium/olive and dark eyes but I look better in warm tones; opposite of what it says I should pick)
Whatever your natural hair color is, go out into the sunlight and look at it there, if the sun shining on it creates purple/blue/green reflections, you have a cool skin tone. If the reflections are gold/copper/red then you probably have a warm skin tone. Whatever your natural hair color's is toned is probably what you should stick with.
From your profile pic you seem like you'd look good in a neutral/warmish color. Like a very pale but full yellow.
I'm gonna recommend Natural Blonde or Butterscotch blonde from the cosplay.com color swatch. I'm leaning towards the natural but I'm also looking at a very small photo of you, and you should have the final say of what you feel comfortable wearing.
Best of luck, I hope this helps!
Cosplays in Progress:
Haruno Sakura (Shippuden)
Theodora (Oz the Great and Powerful)
C. Viper (Street Fighter)
Twilight Princess/BRAWL Zelda (Green BRAWL ver)
Tharja (Fire Emblem Awakening)