From your experience do you think start-up at the early stage should on board director of marketing as a cofounder or chief marketing officer as a cofounder?
In My view Co-Founder manage S&M. Because he will know what his company is trying to sell.
While you most certainly need marketing skills present very early in a business, there is no reason this person needs to be a cofounder. Keep in mind that a cofounder is someone who shares an identical vision for your product/company. Vision is the ideal experience of your product/company for customers, both external and internal. It should not matter whether your cofounder fills a skill gap, though it's lucky when they do.
The first person in a role does not make them a cofounder. And giving out C-level titles in a startup is always a bad idea. Titles should indicate the person has an appropriate level of authority, however C-level titles mean something very specific. They're earned by category experience, not by virtue of being in charge of a department. There are people with 25 years of marketing expertise who are not CMO material.
Understand too that there are 8 divisions of marketing. Even if you have a marketing director, you need the right kind of one. No marketer really becomes an expert in more than 2-3 divisions of marketing.
My advice, reserve board positions and c-level titles for your growth phase. In startup mode use tiles like manager, director, leader. Fill skill gaps with employees, not cofounders. The reason to have a cofounder is to have someone who can be you when you aren't there, to shoulder the same burdens. If you can't pay someone, that's a different issue than trying to find a cofounder.