Pro 750 
HFI-15G
HFI-450
HFI-680
HFI-780
DJ1
iCans 
Zino
Nuforce UF-30 Pro SeriesUltrasone Proline (PRO) 750 headphones 
Pros:Bullet proof.
Well-weighted and well-controlled bass.
Comfortable.
Cons:Full-size Ultrasone headphones aren't dainty!
No carrying case, just a pouch.
Like all Ultrasone's, and amp is preferred.
Summary: Apart from my Sennheiser HD25-I headphones, I consider the Proline 750's (now named
Pro 750) to be my first real shot at proper headphones. These were a total shot in the dark as regards to not having tried them before I bought them. A total leap of faith, which I'm glad I took. In some ways I prefer them to the like of the more expensive Sennheiser HD650, and the Grado SR325i (Grado's being far to one dimensional) headphones. I sold them and now I deeply regret it.
One of the best packages ever including two choices of (screw in) cable, one straight and one coiled (which I love). Replacement ear pads and a nice carrying pouch, although a hard case would be better. But I’m quibbling about nothing, the
Pro 750's are first class.
HFI SeriesHFI-15G 
Pros:The most comfortable headphones I've ever owned!
The S-logic is not as intrusive as others in the Ultrasone range.
Did I mention that they're 'The' most comfortable headphones I've owned?
Cons:Build quality isn't the best
These come a pretty poor 3rd against the Zino's an iCans in the beauty contest.
They do need an amp, but don't go mad.
Summary: To put it bluntly, you're mad, totally bonkers ... if you're looking for a decent pair of portable headphones and you don't by these. Sure the Sennheiser HD238 build quality is better, the AKG K450 have a deeper bass, and the simplistic design of the C-jays wins hands down. But given all that, I'd go home with the
HFI-15G every time.
HFI-15G and amp: As I said before the HFI-15G does benefit from an amp, but don't go nuts. We're not talking about a Ray Samuels; something like the Fiio E3 or E5 does the job admirably.
HFi-450 Pros: For the price, they rock!
Usual Ultrasone build quality.
At a push, you could use them as portables. But expect to get strange looks!
Cons:Usual Ultrasone chunky design (chunky = weighty)
No detachable cable.
Most of you will overlook these.
Summary: Although the HFI-450 are the baby of the range, the sound far exceeded my expectations. Not too heavy in the bass, and they have very good top end control. The Shame is that like the
HFI-15G headphones, these are probably one of the most overlooked in the HFI range.
HFI-680 
Pros:Same build quality as the rest of the full-size Ultrasone range.
At least 95% of the 780's sound quality, but for much less money.
Has to be said, they look nice.
Cons:Ear pads are made from leather made from a Rhinos backside.
No detachable cable.
And yes, they to need an amp.
Summary: So what's the basic difference between the HFI and Pro series? The HFI series are more ... metallic in their presentation. The Pro series offer a smoother, more mature sound. The HFi-680's are a move in the right direction for some, a bit too metalic for others. Choose your music first, and if you find that you lean to electronic music, few others will satisfy as much as the
HFI-680 and HFI780 headphones.
The upper HFI series are more suited to electronic and dance music, rather than Classical or more instruments driven music. And the amp, you could start with the Fiio E5 will do fine.
HFI-780 
Pros:Same build quality as the rest of the full-size Ultrasone range.
One of the best commercial headphones I've heard.
Has to be said, they look nice.
Cons:You would be missing out too much if you bought the HF-680's.
No detachable cable.
And yes, they to need an amp.
Summary: Obviously, there are improvements over the 680's. The
HFI-780's have slightly better top-end and slightly deeper bass. However I wouldn't be disappointed if I could only afford the 680's.
DJ Series DJ1 Pros:Usual Ultrasone quality
Coiled cable (sorry but I love coiled cables).
To avoid the Counterfeit Sony MDR-V700DJ and Pioneer HDJ 1000 headphones, buy the DJ1's.
Cons:They're not subtle
Again no detachable cable
Ear pads could be more forgiving
Summary: Basically, the
Ultrasone DJ1 headphones are HFI-680's on steroids, and I love 'em!
Ultrasone Portable rangeiCans (discontinued) 
Pros:Nice bass.
Good highs.
They're sexier than your average super model.
Cons:Recessed midrange.
Slightly over complicated folding mechanism.
At retail price, some of the variants cost too much.
Summary: These have to be one of the most beautiful headphones on the market, ever. The only issue was that the iCans suffer from a recessed midrange, which was a serious blight on the overall performance.
Regardless of the Zino, the
iCans retailed for $119 against the Zino's $99, and they sound like it!
Zino 
Pros:Nice design
Better build quality than the HFI-15G headphones
Did I say how nice they look?
Cons:The midrange from the iCans remains ..
... albeit covered up by the overblown bass.
Not the kind of sound I was hoping for.
Summary: Unfortunately these were the biggest disappointments of 2009 for me. I was hoping that the
Zino's would clear up the issue of the iCans midrange, but they don't! The midrange issue is still there, but now it's been masked (quite poorly) by the increase of bass. As far as Ultrasone goes, the HFI-15G is still the best sounding portable headphones they have.
I got a slap on the wrist from Ultrasone for my comparison review of the Zino's, iCans and Nuforce UF-30 headphones, via a private message on head-fi.org, but that's too bad. Much as I love Ultrasone and the Zino's fabulous design, I just can't bring myself to recommend them to you.
Ultrasone derivativesNuforce UF-30 Pros:They don’t' sound like the Zino's.
They look like the Zino's.
They're cheaper than the Zino's.
Cons:Against the Zino's, nothing!
Summary: Hands up, the top end isn't as good, and the bass is lighter, but believe me, that's a good thing. And Nuforce has addressed the midrange issue, phew!
