They look good. You might try adding something visually so your thumbnails look like they all came from the same site. This will make your thumbnails stand out more when other videos are suggested to the right of your video. You can check out my thumbs to see what I mean. I've added a solid bar to the right, different colors, but all the videos have it. It makes the thumbs all look like they belong to the same collection. You can see this in some of the bigger youtubers as well like Video Creators.