I'm brand new to the world of high-end headphones, but I love music and want to take my listening experience to the next level. Let me set out my parameters. I'm a college student who's going to be wearing these a lot while studying, so a few things are very important to me. One is portability: I have to be able to take them around, I'll be going back and forth between class and the library all the time. I would prefer closed headphones. Isolation is really important to me (I have to be able to focus in a noisy lounge, when my roommate is playing video games, etc.). Another is minimal leak: I'd like to use them in a library setting, so avoiding leak would be great. And obviously, I want the best sound quality possible within the confines of these parameters, and am willing to make some sacrifices for clearly superior sound quality. As for my musical preferences, I listen mostly to rap and hip hop, though I also listen to alternative and classic rock frequently. I've been considering a few sets, how do they compare based on these parameters? Sennheiser PXC 450 Audio-Technica ATH-M50 Shure SRH750 DJ Beats Studio by Dre How do these measure up? Or are there better options. Thanks in advance for the assistance, this board seems so knowledgeable and helpful.