I think that the best option is to bring a CD to an audio store and listen to some music on a bunch of different headphones. You will want them to be both comfortable and have the sound that you like. As with speakers and electronics. When you are looking at upper end systems, frequently one cannot be characterized as being "better" than the other. Often, they are equally good, but have different "personalities." i.e. one sounds more laid back, the other is quick and aggressive. Neither of these might be better or worse, but you might find that you personally like one more than the other.
crowfan ~ I use the Senn's at work... where people are talking and there is a big copier/printer in the same room. I don't have a problem with the outside noise. I only notice people talkgin when they are right near me, and/or they are talking extremely loudly. I don't even here the big canon copier/printer... (i've tried to listen, both with it on and off and really can't hear it)
The other thing that I like about the open air headphones is that your ears don't get hot and sweaty.
I just noticed that they [senn] have noise canceling headphones. Has anyone had any experience with them? (either from senn or others, are they worth it?)