I have tried both and here is the results
Thrive Content Builder :-
1 - 100x faster
2 - 100x easier
3 - The only real live front page editor there. You edit write on the page, not forms to fill...etc
4 - It generates clean code with no style code in the html page
Visual Composer :-
1 - UNLIMITED VARIATIONS OF ANYTHING YOU COULD IMAGINE
So, it really comes to what you want from it. Are you a web designer who have a lot of clients and want to create a lot of animations, effects, rows backgrounds, and different seperator.. then, you are locked on Visual Composer
However, if you are an IMer's, who want a plugin to help him creating his own website, add posts, hompage customization.. then Thrive Content Builder is the right choice
Note : No matter what your choice is, you are locked on the plugin. If you deactivated any because of stopped support or w/e, then you will lose all the content in Thrive Content, or left with hell of shortcodes and unusable content in Visual Composer
So, if you worry about the future, you might consider Beaver Builder, it doesn't affect your content when deactivated and it has the cleanest, fastest code among them. But of course it comes on the price of features ( Colorful stuff...etc )