K-Mart is going to immediately bolster the bench of a contender and has the potential to put them over the top. He's reportedly deciding between the Clippers, Heat, Knicks, Spurs and Hawks. He isn't what he used to be, but he's still an efficient scorer, rebounder and solid defender that any team in the NBA would be happy as the 3rd or 4th big in a rotation.
According to ESPN, the Clippers and Knicks are likely offering $2.5 million while the rest are closer (or at) the minimum. You have to think the Knicks are playing themselves out of his wishlist, while Atlanta isn't as serious a contender even though they can offer serious minutes as Horford comes into form. The Spurs seem to have an established bigs rotation of Duncan/Blair/Splitter/Bonner so Martin would have to fight for Bonner's minutes, leaving the Clips and Heat. In both cases, he would be the first/best big off the bench (although you could make a Udonis Haslem argument).
Hopefully he decides to go West and make a nasty little 3-man playoff rotation with Blake and Jordan instead of to Miami, but who knows. The 3 Nuggets will be gamechangers and it's something to watch because adding Martin, Smith or Chandler to your bench for the playoffs can plug a serious hole and make a difference. I'd guess the Clippers based on money, potential minutes and impact.