I personally have the S4, and Vsonic GR07 and GR04, using it with sunrise dolphin amp (it's really a no name amp, but I'm traveling and my amp broke down). If I had to put these in a (worst sound to better) gradient, I would say:
GR04 -> Klipsch S4 -> GR07 mkII
However, I'm not too impressed with the build quality in the gr07, especially for the price, the microphonics were too noticeable (the sound of the wires moving, I'm not even sure if that's the right word for it). Actually, they all have pretty bad microphonics.
The GR07 produces a crisp, clear reproduction of sound. However, even with the mass amount of included ear tips, I couldn't find a comfortable fit, but I think my experience here should be the exception, as I really didn't give it a fair try. I'm partially against the GR07 because I almost blew my ears out with them (complete accident). The box said 50 ohms resistance, so when I went from 36 to 50 I figured the volume should be lower. Needless to say, that's a lesson I'll never forget.
Edit: I should mention, the reason I don't use the gr07's is because I like to pair my headphones with an amp, and due to that impedance/volume incident with the '07s, I deemed them too dangerous to my hearing and too cumbersome to carry with an amp and adapters to make it 'work'. Subsequently, my Gf uses them while my portable to-go to's are SE425 & S4
IMO, I would go with the S4, the build qualities nicer and I get much better noise isolation than the VSONICS. However, my purchasing decision would be swayed by whether I had a portable amp or not. The S4's sound much better with a portable amp, whereas the GR07's can be powered by a phone or mobile device without an amp with no problems. If you do decide to amp the GR07's, then I recommend a 75ohm adapter, as the headphones don't scale very well with an amp in terms of volume to Clarity.
Also, the 3.5mm connection side for both headphones seems flimsy to me and the likely 'breaking' point, if you will, of the headphones. The GR07 mkII is slightly better, but not by much.
If you're going to get the GR06, you might as well step up to the GR07's, I think they're much better for the minuscule price difference
Edited by Sushisamurai - 7/31/12 at 11:04am