ATH-M50 or HD25-1 II ?

Hi musicmaker. Well, I used to own HD25-1 and now have the ATH-M50s. In terms of pure SQ alone, I believe that a well burned-in and amped ATH-M50 is better sounding than a stock HD25. The M50s have better extension both high and low. They have some really seriously deep bass that you can feel, especially when amped and their trebles are very smooth and detailed and extend all the way to the maximum that most people can hear without sounding harsh like HD25. However, the M50s need burn in a lot more than HD25s and they need a lot of it. Out of the box, M50s have a really mediocre bass when unamped - it goes deep, but is very undefined and totally lacks tightness. After 50+ hours of burn-in however, you will notice the low end tightening up significantly and the cans will then become suitable for unamped portable use. If you are willing to amp them with a dedicated portable amp on the go however, then I highly recommend that you do that - they will sound really much better out of your MiniBox E+ (which I also have) than they do unamped and bass tightness won't be an issue at all.

Now, ATH-M50 also has a more natural sound than HD25. If you noticed, the piano on HD25 sounds quite unnatural as it has too much weight to it. Well, the ATh-M50 doesn't have that issue and sounds nice and neutral throughout the whole spectrum. It also has a wider soundstage and much better imaging abilities than stock HD25. But again, give the M50s time to burn in to really appreciate the sound as out of the box M50 is quite cold sounding with that flabby bass and also somewhat piercing highs, which really do smooth out after burn-in.

Finally, I may also add that in terms of detail, the HD25 may actually be better in revealing micro-detail and has more texture to the sound. But the difference is really not that big and M50s are still plenty revealing enough to enjoy music and don't really hide anything from you either IMO - they are just a lot smoother than HD25 and maybe that's the reason why they seem to have less detail.

And, of course, in terms of ergonomics, the M50s are definitely better than HD25, as they are circumaural and thus much more comfy, have very good durability (ok, maybe they are not as durable as HD25, but they are still durable enough for most purposes IMO and have metal headband), and while larger in size than HD25, they are still very portable thanks to a great folding mechanism.

Overall, I would say that ATH-M50 is probably the best headphone in its price range overall, offering a great balance of excellent sound quality and good ergonomics. Hope this helps.

EDIT: Sorry, I forgot to talk about the isolation. Unfortunately, M50s won't isolate as well as HD25s, but they offer decent isolation nevertheless. I don't know if they'll work well for use on the plane, as they really don't cut out low end sounds well, but I do use them while commuting on the subway sometimes and they offer enough isolation for me to hear most of the details in the mids and highs, I just turn up the volume a bit.

Pianist, how bout the recessed mid? Is't prominent? For example, compared to triple.fi?

Interesting comments Pianist. I'm in a similar situation as the OP, but isolation isn't really a big priority. A nice warm sound and comfort are what I'm looking for.

How would the ATH-M50 compare to M-Audio Q40, and the Denon D1001?

The ATH-M50 is definitely a step up from the Q40 and D1001 if what Pianist says is true.
I have the HD25-1 and the Creative Live Aurvana! (rebranded D1001) and whole sound spectrum, detail and speed is just way better on the HD25-1.
That about sums it up

that some nice info on the M50!

I have HD25 1 II and D1001, and I disagree about both the detail and speed. Despite the wider soundstage, I enjoy faster classical and rock pieces on HD25. I think this is because HD25 is faster. More dynamic, I think is how someone else described it. And certainly, I hear more detail via HD25 than D1001. That said, I find D1001s more enjoyable for lots of genres of music. Smoother and warmer, more laid back. The HD25s aren't really sibilant cans, but D1001s have smoother highs than HD25. And of course, there's the soundstage.

But then I'm slightly off topic, eh? It's the wine...

That's what I said I said better ON the HD25-1, not better THAN the HD25-1

M50 of course...