It's hard to do wrong in this area. Assuming you'll be spending $150-200 on a HU (not quite entry-level with nice features and room for expansion), performance is very similar. It'll depend mostly on features and aesthetics.
If you held a gun to my head and said to pick one, I'd probably select a
JVC KD-SH55. I've heard nothing but high praise for it, and it's got pleanty of nice features and looks pretty nice too.
[image]http://www.mmxpress.com/jvc/images/KDSH55.jpeg[/image]