^ Haha I am staring at my HD598, Fidelio X2HR, and also the FiiO E17 here now so I feel uniquely qualified to add some thoughts. First up, the X2HR is not as comfortable as the HD598 in my opinion, even with a broken-in support band. The latter is just much lighter and the velour pads are some of the best in the business. Of course this is subjective, but for my average set of ears on an average sized head I dare say my experience will be more common than not. The HD598 is also polarizing in color, but far smaller in footprint too.
Neither of those really need much to drive them, and the E17 is plenty enough for either. The HD598 is more balanced throughout, with the X2HR a lot brighter and more suitable for jazz, pop, and the like. One other thing to point out is the metal magnetic mesh on the exterior of the X2HR cups make for excellent supports for the Antlion Modmic without needing to use the glued-on support pad, so I use the X2HR for a very nice headset.