Do you recommend that Date should be kept in a field with Type of DATE and time kept in a field with type of TIME
or do you recommend that both values be kept together in a field of DATETIME?

And in particular I am referring to when it comes programming the pages in say Php, is it cleaner/faster to have
the date values separate as Date from Time values?

Also is there any practical difference in size & speed between the field having type of DATETIME or TIMESTAMP?