The best replacement for liqueur is liquor.

The best alternatives to liqueur are rated as following:
★★★★★  liquor
★★  cordial
★★  schnapps
★★  brandy
★  triple sec
  grand marnier
  almond extract
  orange extract
  creme de cacao
  peach schnapps

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

Other search terms related to liqueur and their ratings are:

★★★★★ rum
★★★★ aniseed
You have in mind a companion for liqueur and it is not yet here? Propose!

Google Trends

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