I used Visual Composer for a recent project, and I won't do it again. I'm starting to think like Piet on this.
First, Visual Composer renders pages slowly even if you use caching. It's just too heavy and loads too much crap.
Any time you have to display an hourglass to a visitor, or a cutesy animation in its place, you are telling the visitor they have to wait. They don't know how long they have to wait, so they may leave. Bad for conversions!
Secondly, I have run into hosting memory problems when using Visual Composer. A project that ran fine in the previous version of WP now crashes with the current version, and the culprit is that sufficient memory could not be allocated. This was unexpected and very BAD!
So, as Piet says, the best page builder may be none. There are plenty of ways to build excellent websites without one.