I find this to be an easy question, personally.
The easy answer for me to give is in a romantic type of way she loves Kaname more. In fact, I don't think he love for Zero is "romantic" at all.
It had to be kept in mind that there are different types of love.
Romantic, friends, family, etc. I believe her love for Zero is a strong close best friendship love mixed with some family love as well. It is said that only the blood of who you love the most can please your thirst and Yuuki craves for both of their blood, but it never specified if it was just for romantic type of love of not.
It can be easily taken into consideration that Yuuki loves Zero in a friendship/family way just as strongly as she loves Kaname in a romantic way and that is why she craves both of their blood.
Now with all that said, I should probably explain my reasoning on why I think Zeki is friendship/family and Yume is romantic.
The matter of Zeki:
As a human, Zero who was closest to Yuuki. He was a prefect, he knew of vampire's existence, he was adopted as a Cross as well. He also was in the same class as her even. They were together a lot because of this. Being together that long would obviously make them close. Being close could make them very close friends and they could also have a family feel since they were adopted by the same person and were adoptive siblings.
I've never gotten a romantic chemistry vibe off of both of them on both parts, even when they were together a lot with her as a human.
If you have a close friend who is dear to you, naturally you'd want to do a lot for them.
It's not uncommon for very close friends to sometimes develop a type of "crush" on each other or the other. If anything I think Yuuki would just have an innocent close friend crush on Zero, to be perfectly honest.
The matter of Yume:
As a little girl Yuuki made it clear in the memories we saw that she in fact loved Kaname romantically even at that age and wanted to be like "Mommy and Daddy" with him.
As a human she still loved him. I think a safe assumption for this storyline is that she may have still felt the love she had for him hidden in her heart, but she just couldn't remember why.
Yuuki went with Kaname. While they lived together she loved kissing him, drinking his blood, and just being in his arms. She wants to marry him. She accepted being his fiance, it's what she wanted.
Now that he is gone and lying to her she still has faith in him and said she'd wait and do as she wanted as a piece in his game plan until he returned to her. As waiting she is following in his footsteps and accepting all his responsibilities and doing the best she can to become a pureblood Kuran and "hold the fort" while he's doing what he is doing.
Her love for him has shown to be nothing but unconditional.