DC/Greddy combo would be cheaper and would be a complete system since the DC eliminates teh stock midpipe. The Nismo header is nice(its what I have), but combined with the Nismo exhaust, becomes a little loud/raspy and it still uses the stock midpipe.

If I was getting a new system today, I would get the DC header with the APEX'i WS2. Quiet, yet powerful.