The best replacement for d3100 is d5100.

The best alternatives to d3100 are rated as following:
★★★★★  d5100
★★★★  d3200
★★★  d5000
★★★  t3i
★★★  d7000
★★★  t2i
★★★  d90
★★  t3
★★  t1i
★  d40
★  d3300
★  nikon d5000
★  d3000
★  canon t3
★  d80
★  d5200
★  canon t2i
★  1100d
★  d7100
★  k-r
★  nikon d5100
★  canon t3i
★  rebel t2i
★  canon rebel t2i
  nikon d3200
  d5300
  k-x
  d60
  canon t1i
  nikon d90
  rebel t1i
  p510
  d300
  d200
  550d
  lx5
  epl1
  pentax kx

Your alternative for d3100 is not listed? Suggest!
Speaking about d3100, one probably shouldn't forget about 50mm 1.8d.

Other search terms related to d3100 and their ratings are:
★★★★★ 50mm 1.8d
★★ external flash
★★ 50mm
★★ sb700
★ 18 200
★ 50mm lens
★ sb600
tamron lens
lense
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Google Trends

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d3100
d5100
d3200