The best replacement for r407c is r410a.

The best alternatives to r407c are rated as following:
★★★★★  r410a
★★★★  r22
★★★  r134a
★★★  r404a
★  r407a
★  mo99
  r438a
  r417a

Your alternative for r407c is not listed? Suggest!
Speaking about r407c, one probably shouldn't forget about r22.

Other search terms related to r407c and their ratings are:
★★★★★ r22
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r407c
r410a
r22