The answer to this question varies based on a few factors, such as your industry, as well as the product you're selling or the service you provide. In most cases, my clients will use a combination of search ads and social media ads to make sure they have maximum exposure with a cost-effective ROI.
Going "viral" isn't an event you can plan. Any agency or consultant who tells you otherwise is misleading you. Keep in mind, the lightning in a bottle effect is temporary, and a viral video doesn't necessarily translate to long-term success for an individual or a business. With the amount of time you spend trying to come up with a funny video to go viral, you could be implementing a marketing strategy that will consistently drive traffic to ultimately produce leads.
Whether you're considering Google search ads (SEM, PPC) or social media ads, the most popular ad networks tout features and tools promising to simplify and streamline the process of running an ad campaign, but if you don't manually review your ads and devote sufficient time to toggle certain settings before launch AND during a campaign, you won't ensure that your ads are being displayed to the most qualified prospects or in the areas where the ads are most likely to drive conversions and at the most cost-effective rate. None of the major corporations have incentive to continually refine your ads on your behalf, and even if they did, they don't know your audience as well as you.
The leading search engine and social network ad platforms don't care if you sacrifice a few dollars on avoidable inefficiencies, because they count on most businesses being content with the results, since advertisers will always see better ROI than traditional media ads. As any business owner knows, those wasted dollars and cents ad up quickly, and even though AI has come a long way, there will always be certain default ad campaign settings that don't always align with the true purpose or intent of an ad campaign. That's why you need someone who understands your advertising objective and how it aligns with all of the options and settings in the nuances of each respective ad platform.