The best replacement for goodnotes is notability.

The best alternatives to goodnotes are rated as following:
★★★★★  notability
★★★★★  noteshelf
★★★★  penultimate
★★★★  goodreader
★★★  notes plus
★★  zoomnotes
★★  iannotate
★★  notetaker hd
★  upad
★  bamboo paper
  docas
  remarks

Your alternative for goodnotes is not listed? Suggest!
Speaking about goodnotes, one probably shouldn't forget about jot script.

Other search terms related to goodnotes and their ratings are:
★★★★★ jot script
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