What is your favourite tool to (geo) map thing?

If you need to render quite a lot of data look at one of the WebGL implementations, I switched from Leaflet to Maplibre GL for displaying around ~7k linestrings and saw huge performance gains.

Leaflet.js (I've used it through the R and Python libraries)

Leaflet.js is your best bet. It is quick to start, has tons of plugins and can do a lot out of the box.

OpenLayers is probably a little more customizable, but has a steeper learning curve. If you're using PostGIS, you can probably handle much of the less common spatial manipulation there and use Leaflet to render, rather than the client side.

I recently came across Datasette. It lets you a build a map with a simple sqlite DB. Here is an example: https://global-power-plants.datasettes.com/global-power-plan...

Mapbox since they create and host tilesets of my large data and I can spin up a map in minutes.