If your'e an expert, do what you do best.
If your'e a business - obviously you better do both.
SEO - is long term investment to get free quality traffic, ONE DAY.
PPC - is highly scalable, and if you have the winning formula you can copy paste it to other audiences / countries/ products etc.
While with SEO its always from scratch (unless you have a quality PBN and you count it as a future ranking factor)