What is the best disk space analyzer for Windows 10?

Windows can give you a useful first pass without another app. Open Settings > System > Storage and select Show more categories. This separates apps, temporary files, documents, pictures, and system-reserved storage.

For your own files, open PowerShell and run:

Get-ChildItem $env:USERPROFILE -File -Recurse -Force -ErrorAction SilentlyContinue | Sort-Object Length -Descending | Select-Object -First 50 FullName,@{Name='GB';Expression={[math]::Round($_.Length/1GB,2)}}

Use Storage Sense or Disk Cleanup for temporary files. Do not manually delete large items from Windows, Program Files, ProgramData, or WinSxS; remove them through the owning app or Windows cleanup page.