The best replacement for parenthesis is parentheses.

The best alternatives to parenthesis are rated as following:
★★★★★  parentheses
★★★  bracket
★★  brackets
★  after
  parenthesis
  dashes

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

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



Google Trends

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