Probably Nikon Capture though I think it's a dreadful piece of software,
as a rule the manufacturer's software will do best. If you count ease of
use and seamless workflow then it's photoshop. I tend to have a lot of
shots and prefer a smooth workflow so it's photoshop for me. If you just
have a few carefully framed shots destined for poster sized prints and
you have the patience to learn a lame program then capture is your
solution. Other needs & budgets may suggest other programs.

What does best mean for you?

Best color?
Best detail?
Best work flow?
etc, the list goes on.

I've used and use Capture 4.4, PSE3.0/ACR, PSCS2/ACR/ RSE all in different
situations.

It depends on you...

I use Adobe Lightroom (Beta), PS with ACR and Capture NX.
Capture NX gives excellent results but has a slightly annoying interface...

Lightroom (Beta) has serious speed issues but is very nice to use.

I never got on with the RSE interface - it's a personal thing.

Guy

Capture One or Capture One PRO--hands down the best I've used thus far.
Adobe Lightroom is a real piece of crap by comparison.

Bibble has been highly recommended. Personally, I like Aperture 1.5, Nikon
Capture NX, and DxO Pro. DxO Pro has some very interesting capabilities
overall.