Pros: Sounds fantastic, Very comfortable, Sturdy build quality, Attractive aesthetic design, Super portable, Serviceable
Cons: Doesn't isolate, A hair less comfortable than before
This will be a very brief comparison review with the PX100, my review of which can be found here: http://www.head-fi.org/products/sennheiser-px-100-collapsible-headphones/reviews/8181
This is the most striking difference between the PX100 and PX100ii, with the latter being the far better off. The PX100 has aged noticeably, and the updated version really does look far nicer. Sennheiser have updated the aesthetics of a classic without resorting to gaudy, flashy design choices. The PX100ii is sleek, modern, dark and stylish. I think it's a really great looking headphone. I especially like the little Sennheiser logo on the arms, as well as the new cup design. The original PX100 looks a bit cheap in comparison.
Both headphones are very well built for their respective price points, but the more expensive PX100ii improves upon the build at nearly every turn. The PX100ii is a little bit larger and bulkier in it's body, so it feels much nicer in the hands and is better re-enforced. It feels more expensive and a bit fancier, a more premium headphone in it's construction. Both headphones have fantastic durability considering they're such small headphones, but the new PX100ii can old be better in this regard with it's beefed up build. Add to this durability a nice quality finish, and you feel as though you get your money's worth.
Comfort & Ergonomics
The PX100 was previously the only on ear headphone that I considered truly comfortable, and it's now joined by the PX100ii. Both of these on ears are very comfortable. If I had to give the edge to one, it would be the original PX100 for a couple of reasons. Firstly, it's a bit smaller and lighter which gives it's feathery feel (that both models possess) the edge. The other factor is that the articulation of the swivel feature is a little more flexible on the PX100. It seems to align slightly better with the angle of my ear than the PX100ii. However, I should make it clear that these differences are marginal. I still find the PX100ii very comfortable, exceptionally so for an on ear headphone. Ergonomically the two are basically identical, but I'd give a small edge to the PX100ii since it's a single sided cable, which is a little less cumbersome and annoying with portable application.
I heard some very mixed reports about this headphone which almost turned me off buying them entirely. Some very vocal people complained about the new PX100ii sounding vastly inferior to the original.
To my ears, the PX100ii is a tuned up, more refined improvement at every turn of the original. The bass at first sounds like it's actually been toned down slightly, which I think it may have been a hair (and I do mean a hair because the PX100ii is certainly still warm in the bass) but with closer listening I think what makes it sound arguably less in quantity is that it's tighter and more controlled, so it doesn't bloom or bleed the way the PX100 does. The treble response is also improved, in that it seems higher in resolution as well as a bit boosted over the PX100 in quantity. Don't fear though, this is totally un-problematic regarding fatigue. The PX100 is what I'd call dark, and the PX100ii is what I'd call polite. There's more there (and in higher quality) but it's not going to set off anyone's tinnitus. This superior treble response makes the PX100ii more detailed, as well.
While I think the mids themselves sound fairly identical, the clearer treble and more controlled bass does result in there being a more coherent sound through the midrange. Basically the mids are less disturbed than they were before, allowing you to appreciate their quality. The only negative thing I have to say about the PX100ii in the sound department, and I'm nitpicking here, is that it's less efficient than before. I have to turn the volume up one or two notches on my phone to reach the same listening level on the PX100ii as I did with the PX100. However, that's not to say these are hard to drive. You can still reach loud listening levels with these on portable players, just not quite as loud as before.
The PX100ii are an awesome update to one of my favourite headphones. I think they're better in nearly every way, with a few little hairs to split that don't detract from the experience in any significant way. A fantastic portable headphone that leave me way happier and more satisfied as an owner than significantly more expensive (yet flawed) portables that I've owned.