Well, I would start with the one called esc_html()
.
EDIT
Longer answer:
You should perform sanitization on input, and escaping on output.
To sanitize HTML content on input, I would use one of the kses()
family of filters – particularly, wp_kses_post()
, which will filter all but the HTML tags allowed via the Post Editor.
To escape HTML content on output, I would use esc_html()
, which escapes HTML blocks for output.