[phamkl]

On the go? Yes absolutely. That is, if you're going to go somewhere and then sit down in a hotel room or something. 
 
These headphones are pretty cumbersome for use in a subway or on a plane unless you get about a straight 3.5' or so cable with a 3.5mm head and a 2.5 mm head. The stock wire, and the optional straight cable are both too long to take portable and anywhere you're in a public space with a lot of movement, you're going to run the risk of it snagging on this or that or him or her. If you're looking for an out-and-about headphone, I'd check out the Skullcandy Aviators. They look cool and they sound pretty good and they have remote iPod controls (if you have an iPod/Phone.) [note, I recommend these because they're the only other headphone that folds that I have any decent amount of experience with.]
 
If it's the former, though, I definitely recommend the SRH440. 

 

[WTFiretruck]

@ phamkl
thanks for the comment, but I already knew that the cord would be too long, but the cord is detachable and I actually have a couple replacement cords right now. By portability I mostly meant the actual size of the headphones and the ability to fold up (as opposed to the other pair of cans I'm looking at). Sorry I was unclear the first time. But aside from portability, no one in any thread seems to be able to answer my question about whether or not these would be good for easy listening to rock (without amps). So if you could cover the sound quality a bit more that would be great. Thanks

 

[phamkl]

Not having heard any Grados to compare against, I'll say that I like listening to rock on my phones. The 440's are fairly neutral so it'll do all things well (or at least nothing poorly.) In my opinion, these phones are highly detailed and will shine through really complex guitar solos and will still bring out the bassist's hard work. Your cymbals might be just a bit recessed and the kick drum might lose a teensy bit of impact, but the rest of the percussion set will be evident, and all of it is clear.
 
I play my music off of my computer (on board Realtek audio) and off of my Galaxy S2 and it'll do fine with both sources. 

 

[GuitarOverlord]

I'm new on Head-Fi, but I was thinking about the exact same headphones, except I also need to know how well the K121's or the SRH440's work with a guitar amp, a Line 6 Spider IV 75W. I also listen to music that ranges from classical, like Schubert or Paganini, to metal and death metal, like Metallica or Slayer or H.I.M. So can anyone tell me whether the K121 would suit my needs better than the 440's, because I'm kind of leaning towards the 440's, but they've a lower impedance than the 121's, and I'm not too sure about it. I'm split down the middle between these two, and I need to use them for both a guitar amp and just listening on my desktop. Here are the specs for both, if any of you actually need them:
 
http://www.akg.com/site/products/powerslave,id,1111,pid,1111,nodeid,2,_language,EN,view,specs.html
 
http://cdn.shure.com/specification_sheet/upload/147/Spec_Sheet_SRH440.pdf