The best replacement for single quote is double quote.

The best alternatives to single quote are rated as following:
★★★★★  double quote
★★★★★  apostrophe
★★★  double quote php
★  apostrophe keyboard
  double quotes
  backtick

Your alternative for single quote is not listed? Suggest!
Speaking about single quote, one probably shouldn't forget about double quote.

Other search terms related to single quote and their ratings are:
★★★★★ double quote
★★★★ single quote
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Google Trends

Scale is based on the average worldwide traffic of single quote in all years. Click on graph for more.
single quote
double quote
apostrophe