In terms of site optimization PPC and Search optimization is equally important, both of them are major sources to drive quality search traffic to your web site. Where to invest more as per resources are concerned depends on what your long term goals are? Regardless of choice, its very important to have right traffic optimization tools in place for analysis of both Search optimization and PPC Campaigns. This is very important to get you good returns and both of them can each other mutually in one way or the other.
The reason that PPC and search optimization are equally important is because they are both great ways to figure out keyword focused traffic (search focused traffic), which is actually highly relevant to you business and converts into money for you at a later business stage, but the pace for adwords and Search optimization growth is mainly decided by the business goals and resources, keeping them in mind an appropriate web traffic targets can be set.
PPC is designed to generate quick flow of web traffic, but also it requires greater initial investment, testing out PPC also gives you an idea about the performing and good traffic keywords very quickly which can be targeted there after, so its always a good fit to work with PPC and search optimization hand in hand but using PPC as a way of figuring out potential keywords for driving profitable web traffic.