The best replacement for kitkat is jelly bean.

The best alternatives to kitkat are rated as following:
★★★★★  jelly bean
★★★★  ios 7
★★★★  4.3
★★★  cyanogenmod
★★★  ics
★★★  gingerbread
★★  4.2.2
★  ios 7.1
★  jelly bean android
★  jelly bean 4.3
  touchwiz
  windows phone 8.1
  jellbean
  oreo

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

Other search terms related to kitkat and their ratings are:
★★★★★ touchwiz
You have in mind a companion for kitkat and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of kitkat in all years. Click on graph for more.
kitkat
jelly bean
ios 7