Thanks again to all! After reading the replies, I was convinced to get the Amperior, especially after Xallarap's observations.
I don't want to have the feeling after buying that there was a better option out there. After all, I can spent my money once, so I want to do it right.
But after MT0227's reply I'm not that sure anymore . The DT1350 was (and is still) a serious option for me. I read a lot about them. I think most reviews agreed that the Amperior is more 'fun' to listen to (plus a little punchier bass). Besides that, I read it was a bit hard to get a good seal on your ears with the DT1350.
I am recommending the Amperior despite the price difference. Like I said previously, the sound of the HD25 and Amperior are very similar. However, you can never get the refinement of the Amperior even after all the mods done to the HD25, which also adds to the cost. If you can test them all and compare, that would be ideal. But I am under the impression that you don't have that luxury. If this helps, get the HD25 if you're listening mostly to mainstream music, rock, pop, rnb, electronica, etc., get the HD25. If your music collection contains jazz, classical, etc., in addition to mainstream music, the Amperior is the better choice.
On the other hand, I cannot recommend the DT1350. I cannot get the proper fit on them, but despite not getting a good fit, I still found the mids to be good. However, with the lack of proper fitting, the sound was muffled, distant, and soft overall, lacked the fun factor. But that's just me. My friends think highly of them. And yeah, they are well built and I like how the DT1350 looks. I think it's a very classy looking headphone.
Edited by xallarap - 11/20/12 at 3:51am