Which form of marketing is best: PPC, SEO, or Digital Marketing?

PPC and SEO are a part of Digital Marketing. SEO, PPC, display media and content marketing are the strategies used to achieve goals like productivity, etc. You cannot do PPC or SEO without content marketing tactics. Generating more traffic is a vital point.

Digital marketing is main and PPC and SEO is a part of digital marketing

PPC and SEO is also a branch of digital marketing and according to my experience SEO is best than PPC because you can rank your business or website as free and get organic ranking

three of them are best and used for different purposes.
so what are your requirements?  Share it so that we can suggest you the best to go with.

SEO and PPC is part of Internet marketing and both are very important for your website advertisement. I am talking about this and why are important SEO and PPC. SEO is part of digital marketing and this is a slow process but this is effective long time and given long-time result.