In bare stock, pleather form - HD-330 is more comfortable because the pads are softer.
The HD681 and 668B have a harder type of pleather which can become uncomfortable rather quickly (depending on head/ear size).
But once you put velours on them, comfort is no longer an issue. They become genuinely comfy headphones.
In terms of ear room, I think they're similar (hd-330 vs. evo).
Other open cans below 50$ ...
The only one I have direct contact with is the Somic MH463.
In terms of sound alone it's probably one of the best cheap headphones I've owned/listened to.
But comfort in stock form is really bad. The pads are way too shallow and the headband is tensioned a bit too much, so your earlobes end up touching the grille in front of the drivers.
It's a shame really because the pads themselves are soft and the pleather material is nicer than most.
There are however quite a number of pads compatible with this headphone which solve the comfort issue (AT M50 or Shure pads)
Or the diy way - stuffing the underside of the pads with come kind of material (foam, cotton, etc).
Other raved about headphones on the cheap are Takstar hi 2050 and Pioneer Se-A1000.
But I don't have any first hand experience with them yet.
I have ordered a pair of Takstars from aliexpress, which should be arriving soon, but I haven't found a good deal on the Pioneers yet.
From "folklore" they should be both comparable with the Superluxes in terms of raw performance, but come with better comfort and build quality.
The Takstars are supposed to be very similar with DT880 (appearance and fit).
Edited by Bobby S - 3/9/14 at 1:37pm