The best replacement for r12 is r134a.

The best alternatives to r12 are rated as following:
★★★★★  r134a
★★★★★  r22
★★★★  r134
★★★★  134a
★★  11i
★★  r14
★  r20
★  freeze 12
★  r14 insulation
★  r12a
★  r134 refrigerant
  134
  r-134a
  r11
  r22 freon
  mp-t4
  r134a refrigerant
  r414b
  r 134a
  r 134
  r20 insulation

Your alternative for r12 is not listed? Suggest!
Speaking about r12, one probably shouldn't forget about r134a.

Other search terms related to r12 and their ratings are:
★★★★★ r134a
★★★★ 134a
★★★★ r134
★ oaf
★ freeze 12
apex
You have in mind a companion for r12 and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of r12 in all years. Click on graph for more.
r12
r134a
r22