I just got my Kickr Core yesterday, also after training with a dumb trainer. I've been using Zwift and The Sufferfest, and between the two I stay engaged. With Zwift I find the group rides to be a way to stay focused on a ride, and with the Sufferfest the video keeps you going with some of the comments, although once you've done a video a few times it gets repetitive. They are nevertheless well done. I haven't tried Rouvy or the others. If you have an Elemnt or Bolt you can also easily have it control the trainer to simulate your favorite outdoor rides. The more options you have the better to keep you going. Do the trials and my advice would be to pick two so you have options. Isn't your fitness worth about $30/month? Cheaper than a gym in any case.

Also, with any training app, do the special events so you feel like you are part of something, not just riding alone in the garage. I did the Tour of Sufferlandria last year. 9 days of pain, agony and suffering.

I'll add that the Kickr Core is a blast, and very quiet. You can't hear it at all over a fan. And you can't cheat a smart trainer since the instant you let up the resistance increases.