The best replacement for mg4 is m249.

The best alternatives to mg4 are rated as following:
★★★★★  m249
★★★  m240
★★★  m249 bf4
★★★  aws
★★★  m240b
★★  rpd
★★  lsat
★★  type 88
★★  minimi
★  m249 battlefield 4
★  mg3
  fn minimi

Your alternative for mg4 is not listed? Suggest!
Speaking about mg4, one probably shouldn't forget about explosive rounds.

Other search terms related to mg4 and their ratings are:
★★★★★ explosive rounds
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mg4
m249
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