What Is the Best Platform to Collect Video Testimonials?

There's no single best platform. It depends on whether your customers are happy to post publicly. Gleam gives you two routes:

1. Upload: customers send the video file straight to you. Add the Upload action, then set Allowed Upload Types to Video and a File size (MB) limit. Upload is on the Business Plan and above, and it blocks the same file being uploaded twice.
2. YouTube link: if customers already post on YouTube, add Submit a YouTube Video and use Instructions to tell them what to record.

Either way, you can send the videos into a Gallery to show them on your site. Get each customer's permission in your terms before you publish, and ask for a short clip about one concrete result. Those are the easiest to reuse in ads and on landing pages.