The best replacement for 10w30 is 5w30.

The best alternatives to 10w30 are rated as following:
★★★★★  5w30
★★★★  10w40
★★★★  5w20
★★★  20w50
★★★  15w40
★★  sae 30
★★  5w40
★★  20w40
★  10w40 motor oil
★  30w
★  15w50
★  10w40 oil
★  5w30 oil
★  0w40
★  10w20
★  5w30 for winter
  0w20
  10w50
  5w
  20w30
  5w30 high mileage
  0w30
  sae30
  sae
  5w30 synthetic
  10w40 thicker
  5 w30
  10w30
  5w20 oil

Your alternative for 10w30 is not listed? Suggest!
Speaking about 10w30, one probably shouldn't forget about 5w30.

Other search terms related to 10w30 and their ratings are:
★★★★★ 5w30
★★★★ 10w40
★★★★ 5w20
★ 20w50
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