Last year I tried almost all the major Zwift competitor platforms using free trials and coupons and long-story-short, I'm back on Zwift. The only other platform I somewhat enjoyed was Rouvy as it's not really a Zwift competitor in that the appeal is "virtually" riding in places you've never been by watching someone's recorded ride videos versus Zwift's virtual worlds. I'd occasionally see other virtual riders on there, but they were far and few between and the concept of group rides and the like didn't exist.
The problem for other Zwift competitors is that Zwift got such a huge head start that almost all the other platforms hardly have any riders. I got really bored with riding by myself almost all the time in fake/virtual worlds. Then there's platforms like Wahoo's that try to be everything to everyone and in my opinion, fail for everyone. I.e., I'm only interested in a cycling app, not an overall fitness app.