It's a fairly realistic-style skin, so I wouldn't go with any cbutton effect that looks unrealistic. #3 and #5 are pretty unrealistic. #1 would be good if it was without the coloured stroke/outer-glow. #4 would be good, except the shadow is uneven which makes the button appear skewed when you press it. Of the illuminating ones, #2 looks the nicest.
As for the volume, I've never been a fan of those sorts of volumes. At first, it seems pretty cool - like 'hey! I managed to change a horizontal animation into an old-school rotating dial - nifty!'. But the novelty wears off pretty quickly, and you're left with a big list of flaws:
- The user never knows where to click to adjust it. It's very difficult to adjust the volume a bit; you generally need to start from scratch each time.
-it feels unnatural having to operate a dial using a side-to-side motion.
-it's very unspectacular
-only a part of the dial is actually 'clickable'