The best replacement for reason 4 is reason 5.

The best alternatives to reason 4 are rated as following:
★★★★★  reason 5
★★  ableton live 8
★★  logic 8
★★  fl studio 9
★★  reason 3
★  ableton live 7
  fl studio 8

Your alternative for reason 4 is not listed? Suggest!
Speaking about reason 4, one probably shouldn't forget about cubase.

Other search terms related to reason 4 and their ratings are:
★★★★★ cubase
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Google Trends

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reason 4
reason 5
ableton live 8