Cwicly is the best wp builder imo. I'll highlight the features below.

1) Drag and Drop CSS Grid Builder with unique layouts for each breakpoint for static or dynamic items.
2) Ajax Filters. No need to purchase a separate filters plugin.
3) Able to query any wp data.
4) Cloud Design Library. Use, share, sell your work with others.
5) Interactions library.
6) Animations library.
7) Relative Styling - Style inner selectors without writing a code.
8) Modal/Popups.
9) Keyboard/Screen Reader Accessible Menu, Tabs & Accordion Builder.
10) CSS Class Manager to import css classes or stylesheets. SCSS support and folder management.
11) Role Editor. Use it to restrict your clients to only be able to edit text or images or may be you want to allow them to access colors. ;)
12) Modern color picker.
13) Conditional blocks, templates and template parts.
14) WPML and SEO plugins integration.
15) Most important - Fast dev cycle and feedback oriented development.

What else do you need?