Right now? The Nets. The Knicks rely mostly on Carmelo Anthony to be the star, since Stoudemire has rarely been a factor for them, and Chandler is injured. They do have a nice supporting cast (with Shumpert, J.R. Smith, Felton, Bargnani, etc.) and should be doing better, but it's not the same with Brooklyn.
The Nets are the highest paid team in the NBA, they came with high expectations and much boasting. Sure, Williams is injured, but they still have Pierce, Garnett, Johnson, Kirilenko, Lopez, etc. They should be doing way better.