SEO or PPC Advertising?

IMHO, there is no "or" here. I think any marketing function needs to have a presence in both. SEO can be more problem or concept-focused while advertising can be more bottom-of-funnel.

Why not both?

As usual, it depends. But in general, PPC early on to gain traction while building an SEO foundation to make PPC unnecessary.

Both are important, but investing in SEO can also benefit your PPC efforts. Therefore, I prioritize SEO over PPC.

PPC, if you are looking for immediate results. In the longer run, SEO is always the best!

SEO: The users come to you when they are looking for a product they're are already interested in PPC: You nag potential users until they accidentally click on your AD SEO is the winner here.