The best replacement for dx9 is dx11.

The best alternatives to dx9 are rated as following:
★★★★★  dx11
★★★  dx10
★★★  dx8
★★★  dx18
★★  taranis
★★  dx11 wow
★★  dx11 performance
★  dx8 spektrum
★  dx6i
★  aurora 9x
★  11x
★  aurora 9
★  dx11 far cry 3
  dx7
  9503
  dx10 fsx

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Speaking about dx9, one probably shouldn't forget about dx11.

Other search terms related to dx9 and their ratings are:
★★★★★ dx11
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