SEO or PPC Advertising?

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

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.

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!

A foundation on SEO and as @irturko mentioned, PPC early to just gain that initial traction.

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.