The best replacement for nightwing is daredevil.

The best alternatives to nightwing are rated as following:
★★★★★  daredevil
★★★★★  red hood
★★★★  robin
★★★★  gambit
★★★  deathstroke
★★  bane
★★  touring rocket
★★  rocket
★  robin dlc
★  winter soldier
★  jason todd
★  robin arkham city
★  red robin
★  superboy
★  batman beyond
★  batgirl
★  hawkeye
★  cyclops
  robin in batman arkham city
  red arrow
  emerald hippogryph
  slade

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

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



Google Trends

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nightwing
daredevil
red hood