I certainly prefer Grado headphones. I've heard the 580, 580 Jubilee, and 600, and on the Grado end, I've heard the RS-1, RS-2, MS Pro, HP-1, and SR-100. I prefer the increased impact and dynamic sound one gets with Grado headphones; and while some people apparently think that the Sennheisers are more neutral, I believe that they are more colored than some of the better Grados (like my MS Pro or the HP-1). The 580 sounds too laid-back for me, as well as having what I would call a "sloppier" bass. That is, while the 580 has a deep bass response, the notes in the nether regions of the frequency spectrum are not so well-defined.
However, the 580 is, overall, certainly on the same level as the higher-end Grados. I haven't heard the SR-125, 225, or 325 enough to compare them to the 580, so I can't comment there. But I think that you should stick with the 580 unless you can audition a Grado and determine it sounds better. Otherwise you may very well sell the Grado you buy for another 580 or 600 just to make sure you didn't miss out on anything.