Aesthetics are a very personal matter, so there's no wrong or right here. But strong opinions are a must.
To the true Federer believers — and may I deign to place myself among your fervid legion — his game is unparalleled in its aesthetic renown, the effortless elegance, the flowing movement, the cool grandeur. To say it is just too beautiful is to spit upon the budding rose and welcome the rugged weeds in its place, an alliance to that which supplants beauty in its gaudy futilitarianism, a stupid determination that asserts that which works harder works better.
To us, Nadal is the complete opposite of what we love, all sweaty brows, slothfully untucked butt-cracks, smelly fingers, grunting and awkward, hard-working but ugly, despoiling the virginal whites of Wimbledon, the sacred lawns with his grease-monkey ethos. That's not say it's not effective — as Michael shrewdly pointed out with his take on Federer — but just that is appeals to different brain centers in the tennis fans' minds.
The keenness in which we approach the matter is both essential to tennis — to our strong love of a certain kind of game; why bother if you're going to embrace a mediocre middle? — and divisive in appreciating other forms. So, as I think is the case with many, I appreciate certain brands of tennis, but I don't love them.
But I love Rogi. Who has a beautiful game that is second? I can't even fathom someone in the same sentence. But I do love Venus, Agassi and Nalbandian, too.