Functional template is used when the applicant has considerable gaps in his work history. These gaps make a bad impression on employer and hence should be hidden. This format is more focused on the skills rather than the experiences of the applicant.
Lastly, you will need to consider the production of your template. Depending on your industry you need to pick the best invoice to suit your needs. For example, you may use an invoice template that you customize electronically and print from the convenience of your office before submitting to your client.