Off the Mixamp 5.8 alone, I had to max out the volume to feel it had sufficient volume. I don't have that problem with the 32ohm.
The 250ohm is quieter with the Mixamp in terms of hiss at a similar decibel level, as to be expected.
They both sounded identical in the RE6 demo in terms of soundstage and directionality.
Now... I tested them with the E17 off the 3DS.
I fired up the Rhythm Thief demo which I'm acquainted with (I WANT THIS GAME, LOL).
Hmm, this is where the 250ohm shows its weakness. The E17 had to be maxed out at full gain, and it sounded choked. The volume was decent, but there was little dynamics, and energy. In comparison, the 32ohm didn't need to be maxed out, and sounded awesome.
Regardless of the very, VERY minute differences, the 32ohm is winning for me. The versatility, energy, and slight clarity over the 250ohm makes it a winner to me.
Now the 250ohm obviousy needs a desktop amp, (IMHO). With the E17, you will get away with some sources, not others. If you're sticking to portfable amps, the 32ohm is the one you want. If you getting a desktop amp, the 250ohm is the no brainer.
Either way, choose whichever suits your setup, and not whether one sounds slightly better than the other, because to be completely honest, they are too similar to truly say one is superior.
Of course, I'll probably spend all of my days off testing, but I'm almost positive the 32ohm is the one I want. It works for everything, whereas the 250ohm is more picky and still sounds pretty identical.