You will get more traffic ofcorce from SEO. From PPC you will get more qualified visitors. But also it depends on how much money you are going to spend on increasing traffic. It will be great to to use PPC and SEO. If I would have limited budget I would deffinately start with SEO.
SEO is needed for every website and it should be done everytimes not just a few times. IT is along term continous goal which never stops. TO continously getting traffics and increase Page rank and alexa rank it's required.
PPC or the pay per click is mainly the advertisement purpose. It can be done in begining to gain more traffic and then slowly can be left our if your SERP is good.It can be use for increment in SERP (i mean improvement).
SEO should be done by all website while PPC is maninly for selling products or services.
If you want traffic then go for SEO, but it takes time(few months), but if you want sales then PPC is best option. Although PPC is helpful to get limited number of visitors but it is paid marketing and more cost is incureed in it with respect to SEO.