All 2" compression drivers wind up using phase plugs--that's due to the size of the diaphragm relative to the highest frequencies that are reproduced having short enough wavelengths that the diameter if the diaphragm starts to become significant.
It's the material that's important: beryllium is 2.43 times less dense than titanium, and is 2.3x stiffer in bending. It also has a tensile yield strength that is almost double that of titanium. See http://www.vueaudio.com/wp-content/uploads/2012/04/ALMA_Europe_Symposium_2011-PAPER_Small.pdf
There is no contest. I'm actually amazed that so many "audiophiles" want to avoid using beryllium diaphragms. To me it's a no-brainer: it's the single most important factor to consider when comparing 2" compression drivers with a single metal diaphragm. If you don't have the money for Be-diaphragm compression drivers, then you also shouldn't have the money for expensive preamps, amplifiers and expensive DACs, IMO. It makes more difference than all of those other components put together in terms of sound quality.
Perhaps there are other articles that are a little more complicated, but nevertheless, more accurate...
Myers Briggs Music Tastes
The Structure of Musical Preferences: A Five-Factor Modelhttp://www.researchgate.net/publication/271509119_THE_INTERNATIONAL_JOURNAL_OF_HUMANITIES__SOCIAL_STUDIES_Young_Adults_Music_and_Psychological_Well-Being_Exploring_the_Prospects
Chris A's post in IR Input port on the back of an AVR was marked as the answer