Hi there,
I like the "Kinda D*cks" thumbnail. It makes me curious to watch it. All the elements of the picture help conveying a single feeling. It does seem a bit clickbaity, but that's exactly what we want though.
The "Grenade Review" on the other hand is a bit cluttered. There are no hints to guide the movement of my focus to different parts of the picture one by one (unlike the other one). The background is filled with objects to the point that there is no empty space left to be counted as a background. I don't know what to expect from the video (unlike the other one).
So, I really like the thumbnail on the right, and I think it will be helpful if you follow the same pattern.