The best replacement for proc mixed is proc glm.

The best alternatives to proc mixed are rated as following:
★★★★★  proc glm
★★  glimmix
★  glm
★  proc genmod
★  proc reg
  proc glimmix

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Speaking about proc mixed, one probably shouldn't forget about repeated measures.

Other search terms related to proc mixed and their ratings are:
★★★★★ repeated measures
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