It's about personal opinion and coding style? Think twice and hit Here, so you can find more about the major differences between the two libraries.
Some mootools code snippets I really like:
Raphaël Icons done with MooTools ART — It would be awesome to have pure resizeable smiley vectors made from the xenWYSIWYG. Mootools art can do this. In addition we could make detailed animated icons, which unlike .gif format limitations (up to 256 color pallete and up to 1 alpha color transparency), will seem more WEB2. See .PNG example here. NOTE: APNG/MNG are not supported by all browsers.
MooEditable — Simpler to customize OO WYSIWYG editor.
More at: http://mootools.net/forge/