This past week we've moved on from just using Tableau and Tableau Prep, and started using Alteryx and Power BI as well for our Calculations & Functions and Data Models sessions. Naturally, then, I've been asking around a bit to see if people here have any preferences, and the results haven't been too surprising, given that TIL started in partnership with Tableau, and only started properly coaching Power BI a few cohorts ago.
Nonetheless, some people were happy to recommend Power BI: one member of DS44 said it was often much faster for putting together a quick dashboard with just a few simple charts and KPIs, and it was mentioned a couple of times how useful Power Query's 'Create Column From Example' feature is. I can certainly confirm this, having used it myself yesterday to convert US format dates to UK ones, doing in thirty seconds something that would have taken me several 'split' and 'join' functions in Alteryx or Tableau Prep.
As for me personally: I've nowhere near enough experience yet to have a favourite (though I did discover today how ugly Power BI can get with data models, where Tableau looked just lovely). Maybe ask me in a few weeks, though.