Cyclist here. I trialed all three (would suggest you do that) and picked TR. Zwift is entertaining distraction and has social elements if you want a substitute for group training rides and lack of racing options due to Covid. Workouts and planning were weak and gamification was gimmicky to me. Sufferfest was better but workouts not as rich as TR and the whole Sufferfest “suffering” brand gestalt was annoying. TR was all business, best for for me as I am all about having a plan and achieving goals and love the calendar and deep library of workouts and no nonsense workouts all about getting results.
Thought about picking up Zwift for distraction during winter days inside and running concurrently with TR for long hours inside but I may just stick with podcasts, music, audiobooks and streaming video.