Apple Pencil Buyer's Guide
Apple offers four different Apple Pencil models at $79, $99, and $129 price points, each with different feature sets and compatibility.
The choice of Apple Pencil depends on the iPad model you have, as some iPads are only compatible with one kind of Apple Pencil, while others support two.
If your iPad model only supports one kind of Apple Pencil, the buying decision is straightforward.
iPads with a Lightning connector are only compatible with the first-generation Apple Pencil, if they support Apple Pencil at all.
Author's summary: Choose Apple Pencil based on iPad model.