I have own the Sennheiser HD 25-1 II for more than 6 years now, and everything is still in perfect condition. I have always love the analytical sound this unit delivers... These have turn to be my personal favorite headphones for tracking live instruments and recording vocals, but I use them to listen to music when traveling, and they are my favorite portable headphones as well.
 
They are not really that confortable, I find them to be a little uneasy to wear for long periods of time, but they isolate really well and sound great with theire slightly v shaped sound signature. I will recomend this headphones for anyone looking to something portable and with great sound isolation.

Great headphones. Seriously, I'm really impresed with the detailed and excellent natural balanced sound that this unit delivers.

I currently own the K712 pro and the K702 65th Anniversary Edition, and both are great, but I think the K702 AE is a little bit better. Although both models perform really similar, I found that the K712 has slightly more bass volume; but the K702 65th Anniversay Edition has a slightly more defined deep bass. The K702/65th also feel more airy and a little bit brighter (without being harsh) when compared to the K712, that would be because of the increased bass of the K712 I believe.
 
Very comfortable when sitting upright, but a bit loose when bending forward or looking down.

I'm not an expert, nor a collector, but the K705 65th Anniversary Edition are the best headphones I have own (Sennheiser HD600, AKG K701 and a lot others closed back). I'm using them to work on my home studio mixes and "masters" as well as to listen to music at home.