Cropping vs trimming vs resizing
Cropping removes pixels from the edges of every frame (space). Trimming removes frames from the start or end of the animation (time) — use the GIF Trimmer for that. Resizing scales the whole picture without removing anything — use the GIF Resizer. Cropping first and resizing second gives the sharpest result.
Aspect-ratio presets match common destinations: 1:1 for avatars and emoji, 9:16 for stories and phone wallpapers (see GIF to Live Photo), and 16:9 for presentations and video thumbnails.
Hiding something instead of cropping it out
If what you want to remove sits in the middle of the frame — a face, a name or an email address — cropping won’t help. Use Blur GIF to blur or pixelate just that area across every frame. To place the cropped GIF on a new background, try the GIF background remover.