Originally Posted by Azathoth
I'll chime in for the custom 3's.
Like Taikero said, they have more of a flat (yet very detailed) response, and quite warm. Bass is more than satisfactory for me, but it's not the primary focus of the custom 3's sound signature. However, in bass-heavy music (death metal that relies heavily on double bass blastbeats, for example) they will showcase the woofer driver, crushing your skull nicely. They also do cymbal crashes and guitar distortion very well.
Their strong point IMHO is detail, they are more than up to the task of handling complicated music such as technical death metal, progressive rock and jazz fusion. Identifying individual instruments within the songs is no problem with these.
If they had a weakness, I guess soundstage/imaging could be better, but it's a minor quibble. Shure olive foamies fit on the custom 3's, but I haven't tried it yet. I'm still waiting for the 10-pack I ordered to arrive, so I can have better isolation with them.
Could not let the Custom 3s sit in the box (since I am getting the Westone 3s, decided I didn't really need the Custom 3s any more). So I unpacked them, and I am pleasantly surprised at their sound, considering some Head-Fi'ers didn't really like their sound nor style (could not get a good seal). Right out of the box, the gels on them worked for me. Decided to keep them, give them to my wife, who had been using the Senn CX 300s, for the small footprint, but complained that they didn't stay in her ears. The Custom 3s will more than stay put.
Anyway, I also own the X10s. For anyone on the fence, I would say the X10s are more to my liking, mainly because of the ease of use and a little more sparkle on the mids/highs. I just love those little buggers, as they are such a pleasure to wear, remove, etc.
Of course, really looking forward to the Westones. Choosing between the X10s and the Custom 3s, to me at least, is a tough one, but if I had to pick one, I would pay the extra $25 (during the sale) and get the X10s. If you can't bring yourself to spend the extra cash, my personal view is the Custom 3s are certainly worth $150 (but not $300).