The best replacement for a57 is a65.

The best alternatives to a57 are rated as following:
★★★★★  a65
★★★★★  a58
★★★★  a77
★★★  a37
★★★  t3i
★★★  a55
★★  t4i
★  a87
★  a53
★  d5100
★  nikon d5100
★  a99
★  canon 600d
★  a15
★  nex 5n
★  canon t3i
  pentax k30
  sony a65
  a580
  nex 5r
  sony a77

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Speaking about a57, one probably shouldn't forget about a87.

Other search terms related to a57 and their ratings are:
★★★★★ a87
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a57
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