I just got my Senn MX-400s and am very happy. They're my first pair that actually stay in my ears.

If you look at the Apple buds, the stem is flat, meaning there's little projection from the stem to the driver. For me, that meant that the stem would touch my outer ear and eventually cause the bud to fall out.

The Senn stems are curved, and give an extra 1/4" of tolerance for deeper ears without having the stem touch the outer ear. The Senn foamies are thicker than Apples as well. For me, that means a better fit.