The best replacement for infiltrator is soldier.

The best alternatives to infiltrator are rated as following:
★★★★★  soldier
★★★★  sentinel
★★★  vanguard
★★★  adept
★★★  frisk noivern
★★  frisk
★★  flash fire chandelure
★★  vanguard me3
★  vanguard me2
★  perforator
★  inner focus
★  frostblade irelia
★  scout hawken
★  tactician emma frost
★  durga
  vanguard mass effect 1
  light assault
  soldier mass effect
  scrapper
  engineer mass effect 2
  vanguard mass effect 3
  scrapper wolverine
  shadowblade

Your alternative for infiltrator is not listed? Suggest!
Speaking about infiltrator, one probably shouldn't forget about darth maul.

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



Google Trends

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infiltrator
soldier
sentinel