The best replacement for starscream is megatron.

The best alternatives to starscream are rated as following:
★★★★★  megatron
★★★  optimus prime
★★★  bumblebee
★★★  galvatron
★★  ironhide
★★  jazz
★★  soundwave
★★  primus
★  shockwave
★  sam
★  blackout
★  rainbow dash
★  ironhide and ratchet
★  megatron armada
★  arcee
  vector prime
  jetfire
  cyclonus
  ratchet

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

Other search terms related to starscream and their ratings are:
★★★★★ waspinator
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starscream
megatron
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