Pluto is (er, was, er might be, whatever) the only planet discovered by an American. In fact, he was a Kansan. I think that regional pride goes a long way to picking your favorite planet.
Earth isn't "out there" so it has no elusiveness, no mystery, even though there are lots of things we still don't know about it. Until Xena, Pluto was the furthest planet, thus eliciting lots of wonder. Even after decades of space exploration, we still don't know what it's surface looks like. For all we know there may be a huge yellow "have a nice day" happy face on it. Or a big neon sign that says in Swahili "you are not here".
Pluto is the "underdog" of all the planets (pun intended). Small, furthest away, least known and therefor least understood. Mercury gets the prestige of being closest. Venus the brightest. Earth the most life-friendly and the prettiest surface. Mars the angriest. Jupiter the biggest. Saturn with the most complex with the rings. Uranus and Neptune are both gas-giants one of which is the most tilted planet. What can we say about Pluto? We know nothing about it except that it has three moons and has the most elliptical and most inclined orbit.
Earth is our mother planet. Pluto is like the young mysterious woman who you have never seen before and enters the room at a dinner party. Unless you are a "mamma's boy" who clings to her apron strings, of course you are drawn to the recent arrival.