This is probably your best resource-

https://www.dcrainmaker.com/2016/11/...pps-guide.html

Based on posts on this and other forums, Zwift has more users so it can be a more interactive experience, while BKool is more flexible though the social aspect is less easily achieved.

YMMV. I have Zwift and am happy to pay $10 per month for it, I see no need to try any other programs.