For random, quick and dirty, ad-hoc plotting tasks my default is GNUPlot[1].
Otherwise I tend to use either Python with matplotlib, or R with ggplot2.
I keep saying I'm going to invest the time to properly learn D3[4] or something similar for doing web-based plotting, but somehow never quite seem to find time to do it. sigh
[3]: https://ggplot2.tidyverse.org/
[4]: https://d3js.org/