On the topic of plotly, as a big user of Dash (which is powered by the former), I would say Arviz is most definitely the better choice, merely for the reason (though not the only one) that it is based on matplotlib, which is superior in its flexibility as compared to plotly.
Where plotly excels is in creating highly interactive, and efficient, graphs on the web, whereas Pymc3 just needs a fuller complement of visualizations in general; so, for now, plotly should be kept in mind for future versions of Pymc when “web-hostable” graphics will be desired.