How can I easily crop a PDF page?

How can I easily crop a PDF page in a given PDF file? I prefer using as little coding as possible, and guess border geometries as little as possible...

There are several options:

1. Crop by point-and-click using a GUI front-end:
   • pdf-quench
   • krop
   • briss
   • PDF scissors
2. Crop by using the command line:
   • pdfcrop command (provided by texlive-extra-utils), using the following arguments: pdfcrop --margins '-30 -30 -250 -150' --clip input.pdf output.pdf (-left -top -right -bottom format).
   • PDFCrop
   • convert -crop command (provided by imagemagick)
   • Ghostscript
3. Crop by writing your own script:
   • Python
   • LaTeX