The best replacement for sourdough is yeast.

The best alternatives to sourdough are rated as following:
★★★★★  yeast
★★★★  white bread
★★★★  wheat bread
★★  rye
★★  multigrain
★★  regular bread
★★  levain
★★  sprouted bread
★★  sourdough
★  rye healthier
★  rye bread
★  french bread
★  whole wheat bread
★  ezekiel bread
  soda bread
  whole grain bread
  yeast bread
  ciabatta

Your alternative for sourdough is not listed? Suggest!
Speaking about sourdough, one probably shouldn't forget about spelt flour.

Other search terms related to sourdough and their ratings are:
★★★★★ spelt flour
★ ryre flour after using a brown rice starter
You have in mind a companion for sourdough and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of sourdough in all years. Click on graph for more.
sourdough
yeast
white bread