I searched to see if this topic had been discussed already, but didn’t see it.
DC Rainmaker did an updated App review, posted March 27th. He, of course, went into great detail on 11 training apps. I haven’t even gotten through all of it. But he openly admits that the two apps he uses are the two top dogs on the market, Zwift and TrainerRoad.
There are obvious pluses and minuses to both, and DC Rainmaker is much more skilled at expounding on these than I, so I recommend his article.
Finally, I can unequivocally call myself a TR Fanboy. I use the app, listen to the podcast, and occasionally browse the forums. TR has undoubtedly made me faster, which for me is a substitute for fitter, which is my actual goal.