my vote is for the 600s, awesomely nice and engaging sound they have, I'm running them along with the Voyager (and soon to try them out along side an Arrow 2.2g) and I also use them with the ZO thrown in there,
and may I just say Holy *hit! I'm find nothing wrong with the freakishly thumping bass, nice and tight without overpowering the mids, the treble is exceptionally bright, to the point where I use the treble reducer setting on the 7th g iPod calssic to help cool it down, and it works out very nice,
the soundstage is just gigantically HUGE!! and it has me looking around to see where in the hell the sounds are coming from???
and to help with the fit and isolation issue, I use Head-Directs large bi-flange tips, jammed way into my ears, and thus NO hint of them having any feelling of them wanting to fall out or even moving around in the slightest, and I really think they contribute to the WONDERFUL sound that they produce, an ultra clear soundstage with super instrument seperation, hugely fun and very engaging to listen to not fatiguing in the slightest, I tried out all the stock tips and they only muffled the sound compared to the clearity that H-Ds b-f tips provide, I wore the hybrids out on a walk once and after 20 min I couldn't wait to get home and swap them back for the b-f tips, yucky patooey pht pht pht, lol, they left a bad taste in my ears,
I listen to them on average 6 hours a day, and even up to 8-10 hours on occasion!! ka sweetness, once I ran out a fully charged ZO, lol, the key to me using and really enjoying the 600s is using the right tips and getting them sealed and seated in properly,
the only other mid-fi IEMs that I have experience with are the TF10s and RE262s, I quickly traded my TF10s for the EX600s, because after owning and hearing the 262s, the TF10s sounded dull and super muddy, and then I luckily traded out the 10s out for the 600s, I then quickly sold the fabulous 262s, because the 600s made the 262s sound super bass light,
and so I find the 600s to possess the best of both, the deep heavy bass without any muddiness, and with the bright treble of the TF10s, and then the clearity and the instrument seperation of the RE262s, and the 600s soundstage is as if it has the combination of both the 262s and TF10s combined, just super clear, defined, spacious and huge!! very nicely balanced with all the areas well represented, bass, mids, and treble,
as I am ever enjoying and loving my ongoing affair with the 600s, still more and more every day!!!
just a stumble bums .03 worth! as I'd rather be ever luck than good!!