HeadRoom BitHead or Nuforce uDac

I could be wrong, but I believe that the dac in the bithead is always powered by the laptop.  The batteries supply the amp side only.  I've owned a bithead for quite a while now and have enjoyed it.  It is amazing how much less noise you can hear versus plugging directly into the macbook pro.  I don't typically use the batteries when it is plugged into the macbook, though.  I can't tell a difference between the sound of it on battery or not using my SE530s. 

Disclaimer:  I am not an audiophile, just a regular user. 

I use the total bithead and find it to be very nice for PC use, which is all I use it for. It can run either USB powered or battery powered out of a computer. The battery power will cut down on a random pop here and there but otherwise I just use the USB power and my pc hasn't had any performance issues.

About the channel imbalance, I did find that it was detectable, but only at levels far, far below normal IEM listening volume. It was a complete non-issue for me.

It depends on if you are also using an external amp. I found the uDAC's sound a little too edgy and unmusical at times compared to my Total Bithead. However, when it's paired with a better amp than the one found inside, it does its job well. So what I'm trying to say is as a stand-alone unit, the Bithead might be better for you. If you plan on getting a better amp down the road, though, the uDAC trumps this as it is more detailed. One thing to keep in mind is that the uDAC has a much lower noise floor (basically total black) so it'll sound better through IEMs and lower impedence cans. You might notice a hiss in the background if you use the Bithead with IEMs and, to a much lesser extent, low-imp cans.