I don't think there is such a thing as "best." If you listen to rap and like your brain rattled and hearing damaged, so that you'll be deaf before you turn 40, you'll find the "best" earphones to be those overly responsive to high amplitude/low frequency waves. If you're a studio engineer, the "best" earphones will be the type that are truly flat. If you're a classical music fan, the best for you will be a set that are precisely balanced, so that no instrument in the orchestra superficailly dominates. And if you live in a noisy environment then a circumaural pair with active noise-canceling set will be best.
If you let me know what kind of music to which you like to listen, I'll be happy to offer my two cents' worth. Mind you, the NAD Viso HP50's are a very nice. But I'd check the resistance of the speakers before I'd buy those: any product that hides its specifications needs to be scrutinized. If they are, say, a whopping 600 ohms, you'll need a powerful amp to drive them. That would just about rule out using them with a portable media player.