LONGTEXT is probably excessive -- it allows data sizes up to 4GB.

MEDIUMTEXT allows 16MB.

TEXT allows 64KB.

TINYTEXT allows only 255 characters.

Very few HTML documents are going to be 64KB in size, so a TEXT ought to be suitable for you. If you really want to be safe, go for a MEDIUMTEXT.

Reference: http://dev.mysql.com/doc/refman/5.0/en/string-type-overview.html