I never looked at CGI's escapeHTML, so I took a peek.

escapeHTML/unescapeHTML only converts a few characters.
That means you you can't place unicode characters in an iso-latin-1 document, only iso-latin-1 characters.
That means any but a few entities won't be understood. For example, it's unable to unescape é, even if it maps to a character in the specified character set.

HTML::Entities is familiar with all entities.
HTML::Entities can numerically encode any range of characters.
HTML::Entities can decode any range of characters.

escapeHTML has some workarounds for browser issues and for " being accidentally omitted from HTML 3.2.