If the modern Athena still has the same personality and mindset as in the past (And I suspect she does), I do not think the other girls stand a chance in winning Hayate's heart, unless she gives up on him willingly and dissapears permanently.
But knowing Hayate, he will probably try to be nice to everyone no matter what happens. However, that still doesn't change the fact that Athena is the only person that he has ever shown true romantic interest in. All scenes with the other lead girls are just moments of blushing, momentary crush, bloopers, friendship, and mis-understandings.
What I find most surprising is that it isn't often that a manga author can introduce a new character so late in the story and manages to make the audience adore that character, and possibly even want them to end up with the protagonist over the other lead girls.
Hayate no Gotoku was first published in 2005, so we've had almost 4 years of Hinagiku, Maria and Nagi...
And being a hardcore Hinagiku fan myself, I'm probably 60% Hinagiku / 40% Athena right now. But that could change in a few weeks depending on what happens... Things havent been this interesting ever since the balcony scene with Hinagiku
