PPC and SEO are different platforms PPC is used for paid marketing and it is not permanent while SEO is organic and clicks are more than a PPC. If you want long-term results, go for SEO. It will take time but the result will be organic and click will be confirmed form search engines.
We all know that SEO takes time to get the results, therefore it is best to kick start both SEO and PPC at once. Though you might have to crunch your numbers for the budget. Here is my approach.
Approach 1: Specially for the new business, supposedly if you're charging client collectively £2000 - Spend £1200 towards PPC and remaining £800 for SEO per month. As the time goes by, and if you're doings things right with SEO, you can reduce PPC monthly cost, and add it into SEO and eventually after 6 months to a year you will only have to worry about the SEO.
Approach 2: Ranking of certain keywords may be difficult therefore I'd like to continue to run PPC, and rest of the keywords can be dealt by SEO.
Your strategy comes down to clients long term commitments, budget, and ROIs. If you do put in some effort in educating client in the beginning, you can certainly device a much better plan that works both for you can your client in a long run.
Both are equally important but SEO is much more effective compared to PPC. SEO helps to rank keywords higher in search engines and helps to gain more traffic and generate leads for your online business.