The X4 is a further refinement of Jaybird's sport earbuds, and both a solid and cheaper alternative to Apple's Powerbeats3. The barrier for sports headphones is simultaneously high and low. In one sense, any headphones will do — you can pick up a cheap Mpow set on Amazon and if you're not picky they should do the trick, at least until they break.

Longevity is what separates good sport headphones from mediocre ones. Unless you're willing to keep spending money, you'll need sweatproofing to keep them from shorting out. They should also fit securely and comfortably enough to last a complete workout, and sound good enough that you enjoy everything you're hearing, even in a loud gym.