Two main differences: PPC you’re paying everytime someone clicks onto your ad, once your budget has been depleted you will lose all visibility.
SEO gets your website ranking organically, below the paid ads, where the majority of searchers tend to click when looking for a result. With SEO, you’re not paying everytime someone clicks onto the website so you don’t have to worry that you miss out on a massive sale minutes after running out of budget.
In regards to which one is best it’s completely dependent on your market and what your digital goals are.
In some industries the CPC per keyword is extremely high, so it simply wouldn’t be cost effective to pay £20, for example, per website visitor. PPC can afford better targeting for your ads, deciding exactly what keywords you want to appear for, where they should appear and who they appear to which is extremely useful especially for those looking to market time-sensitive promotions.
On the flipside with SEO and appearing on the organic listings you’re granted far more scope with the keywords you could potentially be found for if Google deems you relevant enough.
As 15% of searches made on Google per day are completely new, SEO can help your product/service ro appear in searches that you never knew could be important for your business.
SEO and PPC isn’t a case of either / or, many companies utilise both to maximise their websites visibility.