The best replacement for aquaman is namor.

The best alternatives to aquaman are rated as following:
★★★★★  namor
★★★  submariner
★★  wonder woman
★★  green lantern
★  black manta
★  shazam
★  martian manhunter
★  cyborg
★  ocean master
★  mer-man
  sub mariner
  merman
  human torch
  hawkman
  namor the submariner
  aquaman

Your alternative for aquaman is not listed? Suggest!
Speaking about aquaman, one probably shouldn't forget about justice league.

Other search terms related to aquaman and their ratings are:
★★★★★ justice league
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aquaman
namor
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