Well, I'm not really a guy for homosexual stuff (no offense to anyone, it's just not my thing) so to see her paired with Rei or more likely Hikari seems weird. Especially when Asuka is not hinted to be attracted to the same sex at all in the series (unlike Kagami and Konata, for example.
Now, I hate Shinji, because of his personality. i found him very undesirable, and for me to see him paired with Asuka is a two way thing for me. First I don't like it because I don't believe he deserves her; yet at the same time, she's hinted to have feelings for Shinji in the series, and in teh pictures they're shown in, they can look very cute. It doesn't help Shinji looks just like me if I take off my glasses. I can't help but feel "I am Shinji" when I see them.(eww)