Ever wonder if “funner” is a word?
The adjective fun is an interesting case. You might naturally expect its comparative form to be funner and the superlative to be funnest. However, for a long time, these words were considered non-standard, with more fun and most fun regarded as the correct forms.
The reasoning behind this rule, however, is now obsolete (it has a lot to do with the way fun became an adjective), but the stigma against funner and funnest remains. While the tides are beginning to change, it’s safest to stick to more fun and most fun in formal situations (such as in academic writing or in professional correspondence).