What's the difference between Voxel Elements vs Elementor?

Voxel Elements is faster, while the official Elementor plugin has better compatibility with 3rd party addons.

Voxel Elements is a custom version of the free Elementor page builder plugin, optimized for better performance.

These performance benefits are gained by making changes to the page rendering algorithm, speeding up page loading.
VXE does not make changes to the assets loaded or DOM output.