I haven't spent a million bucks on IEMs. No customs. No triple armatures. But I have made what I feel is a logical progression, from earbud noob to junior audiophile, via way of Sony Ex70s in 2003, to Senn CX300s a couple of years later, to Apple In-Ear (dual arms) to Denon C700s, to my current x10is.
As one web review so vividly put it, the x10is are like a spinal tap into your music.
Especially in the mic/button phone friendly category, I strongly feel there is no better combination of sound quality and comfort. I'd go so far as to say the x10s are the most comfortable buds on the planet.
I won't delve into the micro specifics of fit or sound, as the bountiful reviews out there do a great job of that, but if you are unfamiliar with the x10is, they're a fantastic combination of analytical and punchy. The bass is almost bottomless, but not cartoonish. Mids are a bit recessed, but this is likely due to the tiny driver size, and given the comfort level, it's a totally justified trade off.
I would be thrilled to find a better sounding, equally/more comfortable IEM with a mic and button controls, but from what I can tell, it doesn't exist.
My only complaints about the x10i are the seemingly flimsy cables and the too-long mic/button housing which sits at the center of the Y on the cable. I would prefer a left side mounted housing, placing the mic closer to my mouth for phone use. As it stands, I have to manually hold the mic to my mouth to be heard clearly.