The best replacement for optimus is megatron.

The best alternatives to optimus are rated as following:
★★★★★  megatron
★★★  intercept
★★  fallen
★★  sentinel
★★  rodimus
★★  shockwave
★★  galvatron
★★  samsung galaxy
★  transform
★  unicron
★  grimlock
★  driller
★  predaking
★  megatron prime
★  msr
★  starscream
★  bone crusher
★  jetboil
★  samsung intercept
★  huawei ascend
★  samsung transform
★  ascend
★  hero
★  demolisher
  zio
  nokia lumia
  megatron fall of cybertron
  rodimus prime
  devastator
  comet
  lg motion
  optimus
  stoeger x20
  sanyo zio
  samsung galaxy centura
  moment
  bonecrusher
  sentinel prime
  htc hero
  htc wildfire

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

Other search terms related to optimus and their ratings are:
★★★★★ jetfire
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Google Trends

Scale is based on the average worldwide traffic of optimus in all years. Click on graph for more.
optimus
megatron
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