No matter which strategy you chose, the final goal is to gain exposure📸 in the Search Engine Result Page(SERP). Therefore, it is necessary to understand the mechanism of SERP.
When user type in keywords, SERP will list out all relevant results, and sort by popularity and relevance. More related keywords or higher click-rate, higher ranking of the page🔝. Keywords and click-rate🖱️ is crucial for exposing in SERP.
The main difference between SEM and SEO is that SEM is a paid strategy💸. If you have put lots of time and budget on building your brand and website but not receiving a satisfying result🤦. You may try to use SEM and SEO simultaneously for increasing the exposure of your website.
If you need exposure as soon as possible📈, SEM would be your best choice.