The best replacement for stsadm is powershell.

The best alternatives to stsadm are rated as following:
★★★★★  powershell
★★  powershell sharepoint 2010

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Speaking about stsadm, one probably shouldn't forget about wsp.

Other search terms related to stsadm and their ratings are:
★★★★★ wsp
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stsadm
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powershell sharepoint 2010