I'm taking not one, not two, not three, but four pairs of headphones to MWC.
Two are Bluetooth with different bud sizes and convenience factors (Sony Smart Wireless Headset Pro and Jaybird Bluebuds X). For example, the Sony ones have such small buds, I can actually sleep in them and rest the ear flat on a surface without pain. They are more cumbersome, however, so I'm going to use the Bluebuds X most of the time.
The other two are wired (V-Moda Crossfade M-100 and my trusty Ultimate Ears Super Fi 5 Pro). The M-100 is absolutely amazing, though bulky, but the sound isolation, sound quality, and overall feeling of awesome are hard to beat. The UEs I probably won't use at all, they're just for backup.
Why am I lugging all these around with me? For science, that's why!