Is it advisable to use $post->comment_count instead of get_comments_number( $post_id )

This is that classic question, do you have 6 eggs or half a dozen, and frankly, it doesn’t actually matter.

It is however better to use get_comments_number() because

• the post object is retrieved from the $GLOBALS['post'] global which is set by the_post() inside the loop

• the post object is validated through WP_Post (through get_post())

• the output from get_comments_number() is filterable should you later need to filter the output